The BOREAS Information System
1.1 Data Set Identification
Advanced Solid-state Array Spectroradiometer (ASAS) Level 1b
1.2 Data Set Introduction
(fill in)
1.3 Objective/Purpose
Collect hyperspectral, multiangle data during several field campaigns for a
variety of purposes -- FFC-T objectives: develop capabilities to remotely
monitor the state of the snowpack in the boreal forest; study the
bidirectional reflectance properties of snow and boreal forest canopies with a
snow background; obtain bidirectional reflectance data for early season, to
contribute to phenology (along with datasets from IFCs 1-3). IFC1-3
objectives: study the bidirectional reflectanceproperties of boreal forest
canopies, including phenological variations. Simulate MISR data by acquiring
data at MISR view zenith angles.
1.4 Summary of Parameters
ASAS measures at-sensor radiance of surfaces as a function of spectral
wavelength, view geometry (combinations of view zenith angle, view azimuth
angle, solar zenith angle, and solar azimuth angle), and altitude.
1.5 Discussion
The main objectives of the Boreal Ecosystem Atmosphere Study (BOREAS)
conducted in Canada throughout 1994 are to improve process models which
describe the exchanges of energy, water, carbon, and trace constituents
between the boreal forest and the atmosphere, and to develop methods for
applying the process models over large spatial scales using remote sensing and
other integrative modeling techniques. The Remote Sensing Science Group, of
which ASAS is a part, is responsible for developing linkages between optical
and microwave remote sensing and boreal zone biophysical parameters at various
scales (leaf, canopy, and regional) using measurements from field, aircraft
and satellite sensors plus a range of radiative transfer models.
The experiment strategy for ASAS was to image the Flux Tower sites during each
of four field campaigns. ASAS coordinated with PARABOLA on the ground and
other remote sensing instruments (such as CASI, AVIRIS and MAS) when and where
possible. For each site, three sets of multiangle data were collected by
flying three flightlines in azimuths parallel, perpendicular, and oblique to
the solar principal plane.View angles corresponding to MISR angles were
obtained for a numberof datasets.
1.6 Related Data Sets
AVIRIS CASI MMR PARABOLA SE-590
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2.1 Investigator(s) Name and Title
James R. Irons
Code 923
NASA/GSFC
Greenbelt, MD 20771
2.2 Title of Investigation
Terrestrial ecosystem studies of the boreal forest using bidirectional
reflectances acquired by a hyperspectral, multiangle imaging spectroradiometer
2.3 Contact Information
Carol Russell Code 923 NASA/GSFC Greenbelt, MD 20771 301-286-9416 carol_russell@gsfc.nasa.govMichael Bur Code 923 NASA/GSFC Greenbelt, MD 20771 301-286-8424 bur@gyrfalcon.gsfc.nasa.gov
ASAS is an airborne imaging spectroradiometer that was modified to point off-
nadir by NASA/GSFC for the purpose of remotely observing directional
anisotropy of solar radiance reflected from terrestrial surfaces. The
instrument is capable of off-nadir pointing from approximately 70 degrees
forward to 55 degrees aft along-track (in the direction of flight). As the
aircraft passes over the ground target, digital radiance measurements of the
target are recorded for a discrete sequence of fore-to-aft view zenith angles
within this range. The terms "tilt", "look", or "view" angles are used
interchangeably when referring to the ASAS view zenith angles. For the BOREAS
data collection flights, ASAS imaged most study sites at 8 different view
zenith angles: +70, +60, +45, +26, nadir, -26, -45, -55 degrees.
For the FFC-T datasets, two additional view angles at +15 and -15 degrees were
also acquired. Imaging of sites in the 70-degree off-nadir view angle is
problematic, and this particular angle may or may not be available in every
dataset. Data were acquired in 62 spectral bands ranging from 404 - 1023 nm
with a spectral resolution of approximately 10 nm in each band.
See sections below for further details.
4.1 Sensor/Instrument Description
The ASAS instrument employs a cooled 1024x1024 element silicon charge-coupled-
device (CCD) detector array to generate multispectral digital image data in a
pushbroom mode. The first 324 rows of the CCD are masked. The next 186 rows
are exposed to the output from the spectrometer. The final 516 rows are
masked and used for readout of the array. Two of the rows under the mask
collect smear data which are used to remove smear effects and dark current
from the data.
During the BOREAS missions the operating method of the array was to bin every 3 rows into one spectral band, which resulted in 62 spectral channels. In
addition, every 2 detectors within each row were binned resulting in 512
pixels (per row or line) in the output image data.
In this configuration the spectral band centers, which range from 404 to 1023
nm, are spaced at aproximately 10 nm. Each spectral band has a full-width-
half-maximum of approximately 10 nm.
4.1.1 Collection Environment
The ASAS instrument is mounted on the underside of the platform aircraft
fuselage with the sensor optics either slightly protruding into the slipstream
or retracted into the fuselage pressure box, depending on the view angle. As
the aircraft approaches the target site from a distance, the ASAS instrument
is pointed forward-looking. A video camera bore-sighted with the ASAS optical
head relays a picture to an onboard monitor screen at the ASAS operators'
station. This enables the operator to identify the site and continue tracking
it through a sequence of view angles as the aircraft proceeds on a flight line
over the site. When the site comes into view on the forward point, the
operator begins the data acquisition. The sequence is timed such that the view
is at nadir when the aircraft is directly over the site, and aft-looking views
are taken after passing the site. Determining which views are forwardscatter
or backscatter requires examination of the aircraft heading and the solar
azimuth angle, given in the ASAS ASCII header.
During the 1994 BOREAS missions data were acquired as follows: Flux Towers -
view azimuths parallel, perpendicular and oblique to the solar principal
plane; multiple view zenith angles. Transect or Modeling Sub-Area Mapping
Grids - nadir view zenith angle.
As the platform aircraft flies forward, each row of 512 detector bins is
electronically scanned to generate 62 spectral channels of digital image data
in a pushbroom mode. The signals generated by the CCD detectors are sampled at
a rate of 38 frame lines per second to produce the along-track dimension of
the imagery (image lines). The sampled signal from each detector is digitized
to 12 bits and the digital data are stored on a high-density S-VHS format tape
using a buffered VLDS data recorder.
4.1.2 Source/Platform
NASA/Ames Research Center C-130 Earth Resources Aircraft.
4.1.3 Source/Platform Mission Objectives
Collected hyperspectral, multiangle bidirectional reflectance data (acquired
as at-sensor radiances) over flux tower sites for study of boreal forest
canopies and simulation of MISR data by obtaining measurements at MISR view
angles. Nadir hyperspectral data were acquired over the modelling sub-areas
in each study area and on transects between the Southern and Northern Study
Areas. Hyperspectral, multiangle data were also collected over a calibration
target in the Southern Study Area.
4.1.4 Key Variables
ASAS measures at-sensor spectral radiance in the visible and near-infrared
portion of the spectrum as a function of view geometry.
4.1.5 Principles of Operation
The ASAS optical head is mounted in an open port in the underside of the C-130B aircraft. A complex pointing mechanism incorporating a gimbal enables
the sensor to view off-nadir, facilitating movement in the horizontal,
vertical, rotational fore and aft, and yaw directions.
As the aircraft approaches the target site from a distance, the ASAS
instrument is pointed forward-looking. A video camera mounted adjacent to the
ASAS optical head relays a picture to an onboard monitor screen at the ASAS
operator's station. This enables the operator to identify the site and
continue tracking it through a sequence of view angles as the aircraft
proceeds on a flight line over the site. When the site comes into view on the
first forward angle, the operator initiates the data acquisition process. The
sequence is timed such that the view is at nadir when the aircraft is directly
over the site, and aft-looking views are taken after passing the site.
Yaw compensation can be performed by the operator (if necessary) to prevent
the site from drifting out of the field of view.
As the platform aircraft flies forward, each row of 1024x186 array elements
are electronically scanned to generate 62 spectral channels of digital image
data in a pushbroom mode. The signals generated by the CCD detectors are
sampled at a rate of 38 frame lines per second to produce the along-track
dimension of the imagery (image lines). The sampled signal from each detector
is digitized to 12 bits and the digital data are stored on a high-density S-
VHS format tape using a buffered VLDS data recorder.
4.1.6 Sensor/Instrument Measurement Geometry
Radiation incident on the ASAS aperture is focused onto an entrance slit by an
f/1.4 objective lens with a 57.2 mm focal length. The entrance slit is 50 um
wide across-track, and 23 um wide along-track. The lens focuses incoming
energy through the entrance slit into a 1:1 relay with an effective
focallength of 76.3 mm in each half. In each half of the relay, a 90-degree
mirror prism folds the optical path to create a compact optical head. A
transmission grating ruled at 75 lines per mm and blazed at 530 nm is located
between the two prisms to disperse the radiant energy into its wavelength
spectrum, which is in turn directed by the second prism onto the 186 rows of
the array in the focal plane, where the CCD was mounted.
The instantaneous field-of-view (IFOV) of an ASAS pixel is a function of
optics, detector dimensions, tilt angle (view angle), and aircraft altitude
and attitude (pitch and roll). The optical system includes an f/1.4 objective
lens with a 57.2 mm focal length, providing an 0.33 rad (19.3-degree) total
angular across-track field-of-view. The individual angular resolution of the
center detectors is 0.66 mrad across-track. The along-track field-of-view is 0.44 mrad.
Each detector has dimensions of 19.0 micrometers spatially (across-track) and 19.0 micrometers spectrally, however with a binning factor of 2 in the spatial
dimension and 3 in the spectral dimension, the resulting array pixel size is 38.0 micrometers in the spatial dimension and 57 micrometers in the spectral
dimension.
See Section 6.2.2 for spatial resolution.
4.1.7 Manufacturer of Sensor/Instrument
The ASAS instrument evolved over a number of years. The original optics,
built by TRW, were part of the Scanning Imaging Spectroradiometer (SIS)
constructed in the early 1970s for NASA's Johnson Space Center. ASAS was
created in 1981 when a charge-injection-device (CID) silicon detector array,
made by GE, was incorporated with the optical system for a joint program
involving NASA/JSC and the Naval Ocean Systems Center. In 1984, the sensor
was transferred to NASA/GSFC, where the aircraft mounting bracket was modified
for off-nadir pointing.
In late 1991, the pointing mechanism was upgraded by NASA/GSFC to allow view
angles of 70 degrees forward to 55 degrees aft, and to enable operator-
controlled aircraft yaw compensation. In 1992, the CID was replaced with a
Thomson CSF Model TH7896A (high speed version) charge-coupled-device (CCD)
silicon detector array. BOREAS data were acquired with this CCD array.
4.2 Calibration
Radiometric Calibration
Radiometric calibration data for the BOREAS experiment were acquired from two
primary calibration sources: 1) a 1.2 m diameter integrating hemisphere in the
NASA/GSFC calibration laboratory, and 2) a 30-inch (.76 m) diameter portable
hemisphere that is owned and operated by GSFC. The latter source was used for
in-situ calibration data acquisition since it could be positioned directly
under the aircraft-mounted instrument. The integrating hemisphere is operated
and maintained by the Sensor Development and Characterization Branch at
NASA/GSFC. Up to 12 levels of radiance can be provided for calibration by
turning the internal tungsten filament lamps on or off. The hemisphere is
calibrated on an absolute scale by comparison to the output from a National
Institute of Standards and Technology traceable calibration lamp using a
laboratory-based transfer spectroradiometer. In a calibration run, ASAS is
exposed to a 12-level sequence of spectral radiance levels from the
hemisphere. Dark current (the response of the instrument under conditions of
no incident radiation) is also acquired.
The portable hemisphere can provide up to six different radiance levels in
addition to dark current, however during the BOREAS field campaigns of 1994
only three levels were operating: that provided by three 30-Watt tungsten
lamps. For calibration of the portablehemisphere, contact Brian Markham or
John Schafer of NASA/GSFC.
The digitized response of each detector was recorded for each calibration
source intensity level by selectively controlling the number of lamps turned
on. When possible, data were acquired with the instrument or the portable
hemisphere positioned at two different orientations, opposed by 180 degrees,
to account for any non-uniformities in the reflective surface of the
hemisphere. In some instances, four different orientations, opposed by 90
degrees, were used. Calibration data were acquired for each optical filter
combination (at least 4) used by ASAS during the BOREAS field campaigns.
To derive calibration coefficients, first the data acquired at each
instrument-hemisphere orientation are averaged together. Next, a weighted
average of two channels of smear data are subtracted from each raw digital
number to remove dark current and "contamination" signal generated during
readout of the detector array. This weighting is based on the proximity of
each channel of data to the smear channels which occur in the first and last
channel. Lastly, for eachof the 31744 detectors, a least-squares regression is
performed between the smear-corrected ASAS calibration data and the known
radiance values from the calibration source. This results in a linear
radiometric response function which is inverted to obtain a gain factor.
A radiometric resolution factor is computed for each spectral band by
inverting the mean gain per band. The radiometric resolution factors are
provided in each ASAS data file's ASCII header. Dividing each pixel value by
its associated channel-dependent radiometric resolution factor will give an
absolute at-sensor spectral radiance value in units of mW cm-2 sr-1 um-1.
Signal-to-noise ratios are also measured from the radiometric calibration
data. Equations are derived that provide the signal-to-noise ratio as a
function of digital count. These equations are basically second-order
polynomials that characterize progressively higher signal-to-noise ratios with
increasing digital count (until a maximum level is reached). A maximum
signal-to-noise ratio of approximately 600 was obtained from the calibration
data acquired for the BOREAS project.
The appropriate signal-to-noise equation is stored in the ASCII header of each
ASAS image. The header also contains information on how to apply the equation
to either the digital counts (before the radiometric resolution factors are
applied) or to the radiances (after the factors are applied) in each channel.
The signal-to-noise ratios did not vary greatly over the course of the BOREAS
field seasons. Some example signal-to-noise equations applicable to ASAS
BOREAS data can be seen in the SAMPLE header given in Section 8.4.
Spectral Calibration
A McPherson Model 285 0.5 m double monochrometer serves as the spectral
reference source for ASAS. Light from the monochrometer is collimated by a
paraboloid mirror and directed to the ASAS optics. Instrument output is
sampled every 0.5 nm. The band centers have been computed by determining the
centroid of the area under the response curve for each band. Full-width-at-
half-maximums (FWHM) were measured directly from the response curves.
4.2.1 Specifications
ASAS spectral band centers and FWHM's applicable to 1994 BOREAS datasets are
as follows:
Band Center FWHM ---- ------ ---- 1 404.3 9.5 2 413.7 9.5 3 423.2 9.5 4 432.4 10.0 5 441.7 10.0 6 451.4 10.0 7 460.9 10.0 8 470.5 10.0 9 480.3 10.5 10 490.2 10.5 11 500.0 10.0 12 509.7 10.5 13 519.6 10.0 14 529.7 10.5 15 539.9 10.5 16 549.8 10.5 17 559.6 10.0 18 569.4 10.5 19 579.4 10.5 20 589.7 11.0 21 600.0 10.5 22 610.2 11.0 23 620.3 10.5 24 630.4 10.5 25 640.7 11.0 26 650.9 10.5 27 661.1 11.0 28 671.4 10.5 29 681.5 11.0 30 691.6 11.0 31 701.7 11.0 32 711.9 11.0 33 722.1 11.0 34 732.3 11.0 35 742.6 11.0 36 752.9 11.0 37 763.2 11.0 38 773.5 11.0 39 783.8 11.5 40 794.1 11.0 41 804.5 11.0 42 814.9 11.0 43 825.3 11.5 44 835.7 11.0 45 846.0 11.0 46 856.4 11.0 47 866.8 11.0 48 877.2 11.5 49 887.6 11.5 50 897.9 11.0 51 908.3 11.0 52 918.7 11.0 53 929.0 11.0 54 939.5 10.5 55 949.9 11.0 56 960.3 11.0 57 970.7 11.0 58 981.1 11.0 59 991.5 10.5 60 1001.9 10.5 61 1012.2 10.5 62 1022.7 10.5
4.2.1.1 Tolerance
Individual radiometric resolution factors for each spectral band were adopted
in 1989 to account for the variation of silicon detector response as a
function of wavelength. With every detector bin individually calibrated, each
has its own gain, and as a result, its own specific resolution. A mean
resolution (the radiometric resolution factor) is determined for each channel,
to which all 512 detector bins within each channel are scaled. This results in
very slight over-resolution of pixels furthest away from the center, while
pixels proximal to the center are slightly underresolved.
Periodic horizontal striping of low brightness is apparent in some of the ASAS
imagery acquired for BOREAS. This artifact was caused by an internal array
timing problem that resulted in shortened integration times (and lower signal
levels) for some data frames. Efforts have been made to identify and correct
these "low energy" frames but striping may occasionally be visible in some
images, usually at a frequency of every 6-7 lines. For datasets collected over
the Southern Study Area during the FFC-Thaw, the frequency is approximately 29-30 lines.
4.2.2 Frequency of Calibration
In general, ASAS acquires radiometric calibration data at least twice for each
mission, with one calibration set acquired prior to the mission, followed by a
post-mission calibration after the instrument arrives back at GSFC.
Radiometric calibration data were also acquired during each BOREAS field
campaign using the portable integrating hemisphere described elsewhere in this
document. After several months of quality control and related analyses, it was
determined that calibration data acquired on the following dates would be used
to generate the gains for calibration of data acquired during the listed field
campaigns:
Acquisition Date Applicable BOREAS Field Data ---------------- ---------------------------- 01-JUN-94 FFC-Thaw, IFC-1 data 02-AUG-94 IFC-2 data 17-SEP-94 IFC-3 data
Laboratory spectral calibrations of ASAS were performed both before and after the 1994 BOREAS field season. The spectral stability was also checked once in the middle of the field season using a portable helium neon laser. It has been determined that the spectral calibration results from October 13, 1994 are most appropriate for all 1994 BOREAS data sets.
4.2.3 Other Calibration Information
None.
The ASAS instrument is mounted on the underside of the platform aircraft
fuselage with the sensor optics either slightly protruding into the slipstream
or retracted into the fuselage pressure box, depending on the view angle. As
the aircraft approaches the target site from a distance, the ASAS instrument
is pointed forward-looking. A video camera bore-sighted with the ASAS optical
head relays a picture to an onboard monitor screen at the ASAS operators'
station. This enables the operator to identify the site and continue tracking
it through a sequence of view angles as the aircraft proceeds on a flight line
over the site. When the site comes into view on the forward point, the
operator begins the data acquisition. The sequence is timed such that the view
is at nadir when the aircraft is directly over the site, and aft-looking views
are taken after passing the site. Determining which views are forwardscatter
or backscatter requires examination of the aircraft heading and the solar
azimuth angle, given in the ASAS ASCII header.
During the 1994 BOREAS missions data were acquired as follows: Flux Towers -
view azimuths parallel, perpendicular and oblique to the solar principal
plane; multiple view zenith angles. Transect or Modeling Sub-Area Mapping
Grids - nadir view zenith angle.
As the platform aircraft flies forward, each row of 512 detector bins is
electronically scanned to generate 62 spectral channels of digital image data
in a pushbroom mode. The signals generated by the CCD detectors are sampled at
a rate of 38 frame lines per second to produce the along-track dimension of
the imagery (image lines). The sampled signal from each detector is digitized
to 12 bits and the digital data are stored on a high-density S-VHS format tape
using a buffered VLDS data recorder.
6.1 Data Notes
6.2 Field Notes
The ASAS operators do not make extensive notes about field conditions during
missions. ASAS usually is not flown if atmospheric conditions are not
sufficiently clear. If sky conditions are satisfied, it is up to Principal
Investigators to decide if field conditions are appropriate for data
acquisition. Any observations noted by ASAS operators are made at altitude,
and if considered pertinent to the data, are included in the ASAS header
COMMENTS field.
7.1 Spatial Characteristics
The 1994 BOREAS sites acquired by ASAS consisted of 6 Flux Tower sites in the
Southern Study Area (SSA) and 5 Flux Tower sites in the Northern Study Area
(NSA). In addition, data were acquired over a calibration target, and Candle
Lake in the SSA. ASAS BOREAS images of the Flux Tower sites (at a NADIR view)
are typically about 1.5-2.0 km wide and up to several km long.
Nadir data over auxiliary sites may be available in the Modeling Sub-Area
Mapping Grid and Transect Nadir datasets. Routine processing of the Modeling
Sub-Area Grid and Transect datasets is not planned at this time. After Flux
Tower datasets have been provided to BORIS, the Sub-Area and Transect data may
be processed if there are requests from the user community for these data.
7.1.1 Spatial Coverage
FFC-T
Date Study Area_Site No. Flight_lines
---- --------------- ----------------
4/19/94 SSA_OBS 3
SSA_OA 3
SSA_OJP 3
4/20/94 NSA_OBS 3
NSA_OJP 3
NSA_YJP 3
NSA_FEN 3
IFC-1
Date Study Area_Site No. Flight_lines
---- --------------- ----------------
5/26/94 SSA_AVIRIS_CAL 1
5/31/94 SSA_OBS 3
SSA_OA 3
SSA_OJP 3
SSA_CANDLE_LAKE 1
6/01/94 SSA_OBS 3
SSA_OJP 3
SSA_YJP 3
6/04/94 SSA_OJP 3
SSA_FEN 3
6/06/94 SSA_OBS 3
SSA_FEN 3
6/07/94 NSA_OBS 3
NSA_OJP 3
NSA_YJP 3
NSA_FEN 3
6/08/94 NSA_OA 3
IFC-2
Date Study Area_Site No. Flight_lines
---- --------------- ----------------
7/21/94 SSA_OBS 3
SSA_OA 3
SSA_OJP 3
SSA_YJP 3
SSA_FEN 3
7/23/94 SSA_YA 1
SSA_AVIRIS_CAL 1
7/24/94 SSA_OJP 3
SSA_FEN 3
SSA_YA 3
8/04/94 NSA_OBS 3 (smoke)
NSA_OJP 3 (smoke)
IFC-3
Date Study Area_Site No. Flight_lines
---- --------------- ----------------
9/06/94 NSA_OBS 1
NSA_OA 2
9/13/94 SSA_OBS 3
SSA_OJP 3
SSA_YJP 3
SSA_FEN 3
9/16/94 SSA_OA 3
SSA_AVIRIS_CAL 2
SSA_CANDLE_LAKE 1
9/17/94 NSA_OBS 3
NSA_OA 3
NSA_OJP 3
NSA_YJP 3
NSA_FEN 3
7.1.2 Spatial Coverage Map
7.1.3 Spatial Resolution
Across-track direction:
ASAS spatial resolution in the x-direction is a function of the across-track
field of view, view angle, and the altitude of the platform aircraft. The
across-track pixel size (in meters) is given in the header of each ASAS image.
Across-track pixels do not overlap.
Some examples of across-track spatial resolutions:
At a nadir view angle and an altitude of 5000 m AGL (above ground level), the
full-scene acoss-track field of view is 1.7 km, and the individual pixel size
(across-track) is 3.3 m. At a 60-degree off-nadir view angle and an altitude
of 5000 m AGL (above ground level), the full-scene across-track field of view
is 3.4 km, and the individual pixel size (across-track) is 6.6 m.
Along-track direction:
The along-track spatial resolution of an ASAS image pixel is more complicated. Two aspects are involved:
1) the ground footprint size, and
2) the distance over which the footprint is "smeared" as the aircraft
advances.
The ground footprint is determined by the along-track instantaneous field of
view (IFOV) in conjunction with the view angle and aircraft altitude and
attitude (mainly pitch). The IFOV is described in section 5.1.5.
The radiance measurement recorded for a given pixel is representative of the
ground area observed as the pixel footprint moves forward by the ground
distance of one frame (ASAS is a pushbroom scanner). The ground footprint will
be larger for an off-nadir view angle than for a nadir view. For example, at
an altitude of 5000 meters, the footprint in the along-track direction is
approximately 8 meters at a view angle of 60 degrees versus 2 meters for
nadir.
Regardless of how large or small the footprint is, the ground distance over
which a pixel is "smeared" is determined by the data collection rate, i.e.,
aircraft speed divided by the frame rate. Given a fixed frame rate during the
BOREAS data missions of 38 frames per second and a typical aircraft ground
speed of 220 knots, the spacing or smear distance between adjacent frames is
approximately 3 meters. Thus, an along-track footprint of 2 meters at nadir
(using the example above) would be smeared over a distance of 3 meters. This
results in a2-meter overlap and a center-to-center distance of 3 meters
between pixels of adjacent frames. The effective resolution is therefore
limited by the smearing.
All ASAS datasets are oversampled in the along-track direction. This means
that each image line somewhat overlaps the previous line, making the images
appear more elongated than in reality. Images are not over-sampled in the
across-track direction. This frame or line overlap is not corrected for
during operational ground processing.
An along-track (y-direction) pixel size in meters is given in the header of
each ASAS image file. This number is the aircraft speed divided by the frame
rate which equals the smear distance or non-overlap portion of each pixel in
the y-direction. The y-direction pixel size times the number of lines is
approximately equal to the total ground distance imaged by ASAS for a given
view angle.
Some example along-track pixel sizes during BOREAS:
3.1 m (groundspeed = 230 knots)
3.2 m (groundspeed = 235 knots)
NOTE: BOREAS ASAS data were acquired at altitudes of approximately 4600-5800 m above ground for multiangle flux tower data, and 7000-8000 m above ground for nadir transect data.
7.1.4 Projection
7.1.5 Grid Description
7.2 Temporal Characteristics
7.2.1 Temporal Coverage
ASAS data were collected during April, May-June, July-August, and September, 1994. See Section 6.2.1 for specific dates.
7.2.2 Temporal Coverage Map
7.2.3 Temporal Resolution
ASAS site passes may vary slightly in time duration, depending on the length
of the flight line and the aircraft speed. Typically one multi-angle pass over
a site has a time duration of about 5 minutes.
7.3 Data Characteristics
7.3.1 Parameter/Variable
Not Applicable.
7.3.2 Variable Description/Definition
Not Applicable.
7.3.3 Unit of Measurement
Not Applicable.
7.3.4 Data Source
Not Applicable.
7.3.5 Data Range
Not Applicable.
7.4 Sample Data Record
Not Applicable. See section 8.1.
8.1 Data Granularity
(BORIS and ORNL DAAC to fill in)
8.2 Data Format(s)
UNCOMPRESSED DATA
The logical organizational entity for archived ASAS digital imagery is the
site pass, which in the case of the 1994 BOREAS missions consists of 5-11
separate view angle images per site for multiangle data (Flux Towers); or
strips of nadir images (Modeling Sub-Area Mapping Grid or Transect Runs).
Each image file consists of a series of logical records that are 8192 bytes
in length.
The first record contains ASCII header information in a format described
below. Within the header record the logical header components end with a new
line character, enabling easy recognition of the end of each header record
component.
Subsequent records contain calibrated integer*2 data ordered band-
sequentially; that is, all lines for band 1, followed by all lines for band 2,
and so forth for all 62 bands. Each tape record of 8192 bytes contains 8
image records of 1024 bytes. Each of the image records contains 512 pixels
represented by two-byte binary integers ordered in the Sun/UNIX convention
where the highest-order byte comes first.
Each image record of 512 pixels is one image line, and the number of lines per
view angle may vary. The total number of records per file equals the number of
lines in the image times the number of bands (62) plus NUM_HDR_BYTES listed in
the header. There are no end-of-record or other special characters between
logical records.
A complete ASAS ASCII header delivered with BOREAS project data is as follows:EXAMPLE BOREAS ASAS IMAGE HEADER FORMAT (with some explanations added)
ASAS2_HDR_VERSION: 2.83 NUM_HDR_BYTES:8192 FILE_NAME: tilt_+26.cal (see ** below) TYPE_OF_DATA: IN-FLIGHT # #DATE INFORMATION # LOCAL_DATE: 26MAY94 START_DATE_GMT: 26MAY94 17:26:55 STOP_DATE_GMT: 26MAY94 17:27:08 SOLAR_AZIMUTH(deg): 143.7 SOLAR_ZENITH(deg): 38.3 # #IMAGE SIZE INFORMATION # NUM_LINES: 512 - can vary NUM_PIXELS: 512 NUM_BANDS: 62 DATA_TYPE: UNSIGNED INTEGER*2 DATA_ORDERING: SUN UNIX - Based on SunOs 4.1.3 FORMAT: BAND_SEQUENTIAL STARTING_LINE: 31268- From beginning of Level 0 product STARTING_PIXEL:1- From beginning of Level 0 product ACROSS_TRACK_PIXEL_SIZE(m): 4.1 - Based on nadir IFOV, altitude ALONG_TRACK_PIXEL_SIZE(m): 3.2 - Non-overlap portion, based on IMAGE_DESCRIPTION: ground speed, frame rate # #GEOGRAPHIC LOCATION INFORMATION # GLOBAL_REGION: North America COUNTRY: Canada POLITICAL_SUBDIVISION: Saskatchewan GEOGRAPHICAL_REGION: Boreal forest LAT_CENTER: 53.24000 - refers to target site, not image center LON_CENTER: -105.69000- refers to target site, not image center RADIUS(km): 1.346 # #MISSION INFORMATION # PROJECT: BOREAS FLIGHT_PROJ_NUM: 43002 MISSION_NUM: 406 FLIGHT_NUM: 02 LINE_NUM: 601 RUN_NUM: 2 SITE_NUM: 6 - C130 site designation only SITE: SSA AVCAL SITE_DESCRIPTOR: AVIRIS CAL SITE INVESTIGATOR: Dr. J. Irons # #COMMENTS # Perpendicular - relation to solar principal plane # #INSTRUMENT INFORMATION # TILT_ANGLE: 26- view zenith angle, in degrees FRAME_RATE: 38 # #AIRCRAFT INFORMATION # FLIGHT_FACILITY: NASA/AMES PLATFORM: NASA C-130 ALTITUDE_AGL(m): 5608.3 - AGL = above ground level GROUND_SPEED(knots): 240 HEADING(deg): 322 # #PROCESSING INFORMATION # PROCESSING_DATE: 26JUN95 PROCESSING_FACILITY: NASA/GSFC PROCESSING_LEVEL: 1B - EOS designation PROCESSING_HISTORY: dd swapcomp decom borcal energizer hdrstats # - processing programs #CALIBRATION INFORMATION # SPECTRAL_CAL_DATE: 13OCT94 RAD_CAL_DATE: 01JUN94 RAD_CAL_SOURCE: MOBIL_HEMISP SOURCE_CAL_DATE: 31MAY94 S/N_FORMULA_ORDER: 2 - See Section 5.2 A for discussion S/N_FORMULA_COEFFICIENTS of Signal to Noise ratios C0 -1.876e-01 - Coefficients can vary C1 2.761e-01 C2 -1.719e-05
S/N_DESCRIPTION: S/N = C0 + C1*DN + C2*DN^2 (using coefficients above) or S/N = C0 + C1*Radiance + C2*Radiance^2 where C0, C1, and C2 are given in the table below.
UNITS: DN/RAD_RES_FACT = mW cm-2 sr-1 um-1 BAND CENTER FWHM RAD_RES_ RAD_MEAN S/N_MEAN S/N(C0)S/N(C1)S/N(C2) FACT 1 404.3 9.521 0.72 4 -1.876e-01 5.798e+00 -7.581e-03 2 413.7 9.532 1.14 10 -1.876e-01 8.835e+00 -1.760e-02 3 423.2 9.543 1.81 21 -1.876e-01 1.187e+01 -3.178e-02 4 432.4 10.055 2.35 35 -1.876e-01 1.519e+01 -5.200e-02 5 441.7 10.064 3.10 54 -1.876e-01 1.767e+01 -7.041e-02 6 451.4 10.077 3.83 80 -1.876e-01 2.126e+01 -1.019e-01 7 460.9 10.096 4.25 110 -1.876e-01 2.651e+01 -1.584e-01 . . (channels 8 through 58 will be here; S/N ratios highest in middle channels) . 59 991.5 10.514 4.15 16 -1.876e-01 3.865e+00 -3.369e-03 60 1001.9 10.510 4.04 11 -1.876e-01 2.761e+00 -1.719e-03 61 1012.2 10.5 7 3.96 7 -1.876e-01 1.933e+00 -8.423e-04 62 1022.7 10.5 3 3.88 3 -1.876e-01 8.283e-01 -1.547e-04 # #END_HDR - Marks end of header text
** File names are included in the header so we may store them generically on tape if necessary. The naming convention is: tilt_+70.cal- sensor pointed 70 deg forward tilt_+60.cal- sensor pointed 60 deg forward tilt_+45.cal- sensor pointed 45 deg forward tilt_+26.cal- sensor pointed 26 deg forward tilt__00.cal- sensor pointed straight down (nadir) tilt_-26.cal- sensor pointed 26 deg aft tilt_-45.cal- sensor pointed 45 deg aft tilt_-55.cal- sensor pointed 55 deg aft
To determine forward scatter and backward scatter, compare aircraft heading to solar azimuth angle. If the plane was heading into the sun, forward (positive) points are forward scatter and aft (negative) points are backscatter. If the plane was heading away from the sun, forward points are backscatter and aft points are forward scatter.
9.1 Formulae
Not applicable.
9.1.1 Derivation Techniques and Algorithms
Not applicable.
9.2 Data Processing Sequence
9.2.1 Processing Steps
There are six primary steps performed for operational processing of the ASAS
data acquired for the BOREAS 1994 field season. The names of the programs used
are listed below and they are also included in the ASCII header of each ASAS
data set: dd swapcomp decom borcal energizer hdrstats
ASAS measurements are stored on high-density S-VHS format tape using a Metrum
buffered VLDS data recorder. The raw data are transferred to magnetic disk and 8mm tape using a VLDS unit interfaced to a Unix workstation. These data
consist of continual streams of frames in which each frame contains the
combined image data for all 62 input channels and 2 smear data channels plus
header and navigational information (if available) for a single image line.
The data transfer process involves the Unix "dd" utility for reading the raw
data and a program called "swapcomp" for swapping and complementing the bytes
of each 16-bit pixel.
A quicklook image for each sitepass is created by decommutating a single band
of data encompassing all view angles. Line coordinates of each view angle
subset are manually selected, omitting areas of instrument "slew" and non-
coverage of the site.
Next, all bands of each view angle subset in the sitepass are decommutated.
Each line of data is extracted and written to disk in band-sequential format.
Each view angle subset is stored in a separate file with an ASCII header
automatically populated with entries retrieved from an online database
containing information about the specific project and sites.
These image files now consist of a series of logical records 1024 bytes in
length. The first several records store the header information. Subsequent
records contain band-sequential integer*2 data. Each record represents 512
pixels.
Radiometric calibration is performed next using the program "borcal". It
applies the calibration gains derived from the integrating hemisphere lamp
data to each pixel. The output format is identical to the input format except
that the 2 smear bands are removed. The calibration procedure is described in Section 4.2.
The next processing step for ASAS BOREAS data is correction of low energy
frames that resulted from an instrument array signal readout problem. Section 4.2.1 discusses this problem. The program "energizer" attempts to correct the
affected frames. It begins by parsing the data four separate times to
determine which frames fit the criteria for reduced energy or signal levels
caused by the timing problem. The first pass involves the profiling of total
energy versus frame, smoothing the profile to remove high and low frequency
noise, and flagging of suspect frames using a mean value threshold. Subsequent
passes attempt to refine the list of suspect frames based on the expected beat
frequency. For most of the BOREAS data, the beat frequency is every 6-7
frames. After the suspect frames are identified, they are multiplied by a
corrective weighting factor determined from the calibration data.
The last operational processing step is calculation of the mean scene radiance
levels for all bands of each view angle image in a site pass. The
"hdrstats"program computes the mean radiances and stores them in the ASCII
header of each image.
9.2.2 Processing Changes
For the most part, the processing steps outlined in Section 9.2.1 apply to all 1994 BOREAS data sets. However, there are some inter-IFC differences in the
data characteristics:
The data acquired for each IFC will have a specific set of calibration gains,
radiometric resolution factors, and signal to noise ratios.
The frequency of occurrence for the low energy frame striping was every 6-7
lines for all IFC's except for Southern Study Area FFC-Thaw data where the
frequency was approximately 29-30 lines.
For IFC-1, IFC-2, and IFC-3, data were acquired at the following eight view
angles: +70, +60, +45, +26, nadir, -26, -45, -55. For FFC-Thaw, two additional
angles were used: +15, and -15. These angles describe the view angles which
were attempted but not necessarily achieved in all cases.
9.3 Calculations
9.3.1 Special Corrections/Adjustments
9.3.2 Calculated Variables
9.4 Graphs and Plots
Not applicable.
10.1 Sources of Error
Potential sources of uncertainty associated with ASAS spectral radiance
include the following factors: spectral radiance from the integrating
hemisphere; spectral radiance from the portable hemisphere; transfer of
spectral radiance to ASAS detector elements; and spectral calibration of the
ASAS detector elements. Other factors such as polarization sensitivity,
signal cross-talk between detectors, and stray light may contribute to the
uncertainty, but these factors have not been evaluated.
10.2 Quality Assessment
10.2.1 Data Validation by Source
During processing, frequency histograms of selected channels for each view
angle are plotted and examined manually for anomalies. Images are also
displayed and visually analyzed for target coverage, data dropouts, saturation
and other potential problems.
10.2.2 Confidence Level/Accuracy Judgement
The uncertainty associated with ASAS spectral radiance values is approximately 6%. This number is the root-sum-square of the uncertainties contributed by
the following factors: spectral radiance from the integrating hemisphere (5%
uncertainty); transfer of spectral radiance to ASAS detector elements (2%
uncertainty); and spectralcalibration of the ASAS detector elements (1%
uncertainty). The uncertainty associated with the radiance of the portable
hemisphere has not been determined, however it is probably similar to that of
theintegrating hemisphere. Other factors such as polarization sensitivity,
signal cross-talk between detectors, and stray light may contribute to the
uncertainty, but these factors have not been evaluated.
10.2.3 Measurement Error for Parameters
10.2.4 Additional Quality Assessments
Spectral response curves for selected training areas are plotted and examined
for known atmospheric absorption features. These plots are also compared to
similar measurements made by other instruments, if data are available.
10.2.5 Data Verification by Data Center
(For BORIS and ORNL DAAC Use)
11.1 Limitations of the Data
11.2 Known Problems with the Data
Image Data:
Header Information:
11.3 Usage Guidance
At present, the provided ASAS data are not geo-rectified or geo-located, nor
are they corrected for atmospheric effects. Accurate accounting of
atmospheric effects on the at-sensor radiance measurements is very important,
since ASAS data acquisition involves observations through varying path
lengths.
Users should view ASAS images thoroughly in all spectral bands of interest and
select study areas carefully. Check the ASAS ASCII header for each dataset's
appropriate spectral radiometric resolution factors and S/N ratios. Use
special caution working with channels below 490 nm or above 870 nm (See
Section 11.1).
11.4 Other Relevant Information
None.
14.1 Software Description
14.2 Software Access
15.1 Contact Information
15.2 Data Center Identification
15.3 Procedures for Obtaining Data
15.4 Data Center Status/Plans
16.1 Tape Products
16.2 Film Products
16.3 Other Products
17.1 Platform/Sensor/Instrument/Data Processing Documentation
Kovalick, W. and Graham, D., 1991, ASAS Programmer's Manual, Hughes STX, Code
923, NASA/GSFC, Greenbelt, MD. (In-house document)
17.2 Journal Articles and Study Reports
Many of the following articles describe data from the first generation CID
array (prior to 1991). Radiometric resolution factors and spectral band
centers differ among the various ASAS datasets.
Abuelgasim, A. A. and A. Strahler (1994), Modeling bidirectional radiance measurements collected by the Advanced Solid-state Array Spectroradiometer (ASAS) over Oregon Transect conifer forests, Remote Sens. Environ. 47:261-275.
Abuelgasim, A. A., S. Gopal, J. R. Irons, and A. H. Strahler (in press), An artificial neural network for the classification of ASAS directional measurements, Remote Sens. Environ.
Brown de Colstoun, E.C., C.L. Walthall, C.A. Russell, and J.R. Irons (in press), Estimating the fraction of absorbed photosynthetically active radiation (fAPAR) at FIFE with airborne bidirectional spectral reflectance data, J. Geophys. Res..
Deering, D. W., E. M. Middleton, J. R. Irons, B. L. Blad, E. A. Walter-Shea, C. J. Hays, C. L. Walthall, T. F. Eck, S. P. Ahmad, and B. P. Banerjee (1992), Prairie grassland bidirectional reflectances measured by different instruments at the FIFE site, J. Geophys. Res. 97:18887-18903.
Guinness, E.A., R.A. Arvidson, J.R. Irons, and D.J. Harding (1991), Surface scattering properties estimated from modeling airborne multiple emission angle reflectance data, Geophys. Res. Letters 18(11):2051-2054.
Hall, D.K., J.L. Foster, J.R. Irons, and P.W. Dabney (1993), Airborne bidirectional radiances of snow covered surfaces in Montana, USA, Annals of Glaciology 17:35-40.
Irons, J.R., K.J. Ranson, D.L. Williams, R.R. Irish, and F.G. Huegel (1991), An off-nadir pointing imaging spectroradiometer for terrestrial ecosystem studies, IEEE Trans. on Geoscience and Remote Sensing 29(1):66-74.
Lawrence, W. T., D. L. Williams, K. J. Ranson, J. R. Irons, and C. L. Walthall (1994), Comparative analysis of data acquired by three narrow-band airborne spectroradiometers over subboreal vegetation, Remote Sens. Environ. 47:204-215.
Qi, J., M. S. Moran, F. Cabot, and G. Dedieu (in press), Normalization of sun/view angle effects on vegetation indices with bidirectional reflectance function models, Remote Sens. Env.
Johnson, L. F. (1994), Multiple view zenith angle observations of reflectance from ponderosa pine stands, Int. J. Remote Sens. 15: 3859-3865.
Moran, M. S., R. D. Jackson, T. R. Clarke, J. Qi, F. Cabot, K. J. Thome, and P. N. Slater (in press), Reflectance factor retrieval from Landsat TM and SPOT HRV data for bright and dark targets, Remote Sens. Env.
Ranson, K. J., J. R. Irons, and D. L. Williams (1994), Multispectral bidirectional reflectance of northern forest canopies with the Advanced Solid-state Array Spectroradiometer (ASAS), Remote Sens. Env. 47:276-289.
Russell, C. A., C. L. Walthall, J. R. Irons, and E. C. Brown de Colstoun (in press), Comparison of airborne and surface spectral bidirectional reflectance factors, spectral hemispherical reflectance and spectral vegetation indices, J. Geophys. Res.
Schaaf, C. B., and A. H. Strahler (1994), Validation of bidirectional and hemispherical reflectances from a geometric-optical model using ASAS imagery and pyranometer measurements of a spruce forest, Remote Sens. Env. 49:138- 144.
Shepard, M.K., R.E. Arvidson, and E.A. Guinness (1993), Specular scattering on a terrestrial playa and implications for planetary surface studies, J. Geophys. Res. 98(E10):18,707-18,718.
van Leeuwen, W. J. D., A. R. Huete, C. L. Walthall, S. D. Prince, N. P. Hanan, A. Begue, and R. J. Roujean (in review), Deconvolution of remotely sensed spectral mixtures for retrieval of LAI, fAPAR and soil brightness, submitted to J. Hydrology, HAPEX special issue. UNREFEREED CONFERENCE PROCEEDINGS, TALKS, SYMPOSIUMS
Abuelgasim, A. and S. Gopal (1994), Classification of multiangle and multispectral ASAS data using a hybrid neural network model, IGARSS'94 Digest, 3: 1670-1672.
Allison, D., and Muller, J.-P. (1992), An automated system for sub-pixel correction and geocoding of multi-spectral and multi-look aerial imagery, Proc. XVII Congress, Int. Soc. Photogramm. and Rem. Sens., Washington D.C., Aug.2-14, 29(B2) pp. 275-285.
Allison, D., M. J. Barnsley, P. Lewis, N. Dyble and J.-P. Muller (1994), Precise geometric registration of ASAS airborne data for land surface BRDF studies, IGARSS'94 Digest, 3:1655-1657. Birk, R. J., and T. B. McCord (1994), Airborne hyperspectral sensor systems, 47th National Aerospace and Electronics Conf., Dayton, OH, May 23-27.
Brown de Colstoun, E. C., C. L. Walthall, C. A. Russell, and J. R. Irons (1994), Estimating the fraction of absorbed photosynthetically active radiation (fAPAR) from off-nadir airborne measurements, IGARSS'94 Digest, 3: 1823-1825.
Cabot, F., J. Qi, M. S. Moran, and G. Dedieu (1994), Test of surface bidirectional reflectance models with surface measurements: results and consequences for the use of remotely sensed data, Sixth International Symposium on Physical Measurements and Signatures in Remote Sensing, Jan 17- 21, Val d'Isere, France.
Chong-guang, Z., W. Jun, and A. H. Strahler (1994), A new registration algorithm for ASAS multi-angle images, IGARSS'94 Digest, 3:1658- 1660.
Dabney, P. W., J. R. Irons, J. W. Travis, M. S. Kasten, and S. Bhardwaj (1994), Impact of recent enhancements and upgrades of the Advanced Solid- state Array Spectroradiometer (ASAS), IGARSS'94 Digest, 3:1649-1651.
Diner, D. J., S. R. Paradise, and J. Martonchik (1994), Development of an aerosol opacity retrieval algorithm for use with multi-angle land surface images, IGARSS'94 Digest, 3:1664-1666.
Gatlin, J. A., E. M. Middleton, J. R. Irons, and J. W. Robinson (1991), The application of high spectral resolution and spatial resolution imaging spectrometers for locating downed aircraft, Proceedings of the International Geoscience and Remote Sensing Symposium, Espoo, Finland, v. 3: 1363-1366.
Harding, D. J., and J. R. Irons (1990), Bidirectional radiance of playa and volcanic surfaces: Advanced Solidstate Array Spectroradiometer (ASAS) measurements of Lunar Crater volcanic field, Nevada, Proc. of the IGARSS'90 Symposium, Univ. of Maryland, College Park, MD, v.2:1361-1363.
Huete, A. R., H. Y. Liu, and H. Q. Liu (1994), Directional vegetation index interactions in ASAS imagery, IGARSS'94 Digest, 3:1813-1814.
Irons, J. R. and R. R. Irish (1988), Sensor calibration for multiple direction reflectance observations, SPIE Proceedings Vol. 924, Recent Advances in Sensors, Radiometry, and Data Processing for Remote Sensing, p. 109-119.
Irons, J. R., F. G. Huegel, and R. R. Irish (1989), Prairie grass hemispherical reflectances from airborne multi-directional observations, Proc. of 19th Conf. on Agriculture and Forest Meteorology and the Ninth Conf. on Biometeorology and Aerobiology, March 7-10, 1989, Charleston, SC, published by American Meteological Society, Boston, MA.
Irons, J. R., K. J. Ranson, D. L. Williams, and R. R. Irish (1989), Forest and grassland ecosystem studies using the Advanced Solidstate Array Spectroradiometer, Proceedings of the International Geoscience and Remote Sensing Symposium, Vancouver, Canada, v. 3: 1761-1764.
Irons, J. R., P. W. Dabney, J. Paddon, R. R. Irish, and C. A. Russell (1990), Advanced Solidstate Array Spectroradiometer (ASAS) support of 1989 field experiments, SPIE Proceedings Vol. 1298, Imaging Spectroscopy of the Terrestrial Environment, April 16-17, 1990, Orlando, FL.
Irons, J.R., B.W. Meeson, P.W. Dabney, W.M. Kovalick, D.W. Graham, and D.S. Hahn (1992), A data base of ASAS digital image data, Proc. 12th Annual International Geoscience & Remote Sens. Symp., IGARSS'92, Vol. I, Houston, TX, 26-29 May, 1992:517-519.
Johnson, L. F., and D. L. Peterson (1994), Estimation of forest canopy leaf area index using directional ASAS measurements, IGARSS'94 Digest, 3:1819- 1822.
Kovalick, W. M., D. W. Graham, and M. Bur (1994), Data processing and calibration of the Advanced Solid-state Array Spectroradiometer, IGARSS'94 Digest, 3:1652-1654.
Lewis, P., M. J. Barnsley, M. Sutherland, and J. P. Muller (1995), Estimating land surface albedo in the HAPEX-Sahel experiment: Model-based inversions using ASAS data, IGARSS'95 Digest, Florence, Italy, July 10-14, 1995:2221-2223.
Liang, S., and A.H. Strahler (1993), BRDF retrieval from multiangle remotely sensed data, SPIE Proceedings Vol. 1938, Recent Advances in Sensors, Radiometric Calibration, and Processing of Remotely Sensed Data, April 14- 16, 1993, Orlando, FL.
Markham, B. L., J. R. Irons, D. W. Deering, R. N. Halthore, R. R. Irish, R. D. Jackson, M. S. Moran, S. F. Biggar, D. I. Gellman, B. G. Grant, J. M. Palmer, and P. N. Slater (1990), Radiometeric calibration of aircraft and satellite sensors at White Sands, NM, Proceedings of the International Geoscience and Remote Sensing Symposium, College Park, MD, v. 1:515-518.
Martonchik, J. V. and J. E. Conel (1994), Retrieval of surface reflectance and atmospheric properties using ASAS imagery, IGARSS'94 Digest, 3:1661- 1663.
Qi, J., F. Cabot, M. S. Moran, G. Dedieu, and K. J. Thome (1994), Biophysical parameter retrievals using bidirectional measurements, IGARSS'94 Digest, 3:1816-1818, 1994. Schaaf, C. B., X. Li, and A. H. Strahler (1994), Validation of canopy bidirectional reflectance models with ASAS imagery of a spruce forest in Maine, IGARSS'94 Digest, 3:1832-1834.
Staenz, K., R.P. Gauthier, and P.M. Telliet (1993), Bidirectional- reflectance effects derived from ASAS imagery of a pecan orchard, SPIE Proceedings Vol. 1937, Imaging Spectrometry of the Terrestrial Environment, April 14-16, 1993, Orlando, FL.
Teillet, P. M. and J. R. Irons (1990), Spectral variability effects on the atmospheric correction of imaging spectrometer data for surface reflectance retrieval, Proc. of the ISPRS Commission VII Mid-Term Symposium: Global and Environmental Monitoring Techniques and Impacts, Victoria, BC, Canada:579- 583.
van Leeuwen, W. J. D., A. R. Huete, and C. L. Walthall (1994), Biophysical interpretation of a spectral mixture model based on a radiative transfer model and observational data, IGARSS'94 Digest, 3:1458-1460.
CDROM COLLECTIONS
Angelici, G.L., J.W. Skiles, and L.Z. Popovici (1992), OTTER: Oregon
Transect Ecosytem Research Project, Collected Data, Volume 1, Version 1,
Satellite, aircraft and ground measurements, CD-ROM USA_NASA_PLDS_OT_0001,
NASA/ARC.
Arvidson, R.E., Dale-Bannister, M.A., Guinness, E.A., Slavney, S.H., and Stein, T.C., 1991. Archive of Geologic Remote Sensing Field Experiment, Data-Release 1.0, CD-ROM Volume USA_NASA_PDS_GR_001, NASA Planetary Data System, JPL, Pasadena, CA.
Strebel, D.E., D.R. Landis, J.A. Newcomer, B.W. Meeson, P.A. Agbu, and J.M.P. McManus (1992), Collected Data of the First ISLSCP Field Experiment, Volume 4: ASAS & PBMR Imagery 1987 & 1989, CD-ROM USA_NASA_PLDS_FIFE_0004, NASA/GSFC.
17.3 Archive/DBMS Usage Documentation
AGL - Above Ground Level ASAS - Advanced Solid-state Array Spectroradiometer BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System FFC-T - Focused Field Campaign - Thaw FWHM - Full Width Half Maximum GSFC - Goddard Space Flight Center HDR - Header IFC - Intensive Field Campaign IFOV - Instantaneous Field-of-View NASA - National Aeronautics and Space Administration ORNL - Oak Ridge National Laboratory SSP - Solar Principal Plane URL - Uniform Resource Locator
Return to top of document.
20.1 Document Revision Date
Aug-1995
20.2 Document Review Date(s)
BORIS Review:
Science Review:
20.3 Document ID
(For BORIS and ORNL DAAC Use)
20.4 Citation
Acknowledge James R. Irons and Philip W. Dabney for providing ASAS data. Cite
relevant ASAS publications (see Section 12.2).
20.5 Document Curator
(For BORIS and ORNL DAAC Use)
20.6 Document URL
(For BORIS and ORNL DAAC Use)
