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LAI & PAR DATA: LIGHT BAR - UNL (FIFE)
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LAI & PAR Data: Light Bar - UNL (FIFE)

Summary:

The Leaf Area Index and PAR Determined from the UNL Light Bar Data were collected in 1987, 1988, and 1989. Incoming, reflected, and transmitted photosynthetically active radiation (PAR) was measured with a LI-COR LI-191SA line quantum sensor. Absorbed and intercepted PAR calculated from these measurements.

The objectives of this research were to characterize bi-directional reflectance factor distributions, estimate surface albedo, determine the variability of reflected and emitted fluxes in selected spectral wavebands as a function of topography, vegetative community and management practice, determine the influence of plant water status on surface reflectance factors, and determine sun angle affects on radiation fluxes.

Table of Contents:

  1. Data Set Overview
  2. Investigator(s)
  3. Theory of Measurements
  4. Equipment
  5. Data Acquisition Methods
  6. Observations
  7. Data Description
  8. Data Organization
  9. Data Manipulations
  10. Errors
  11. Notes
  12. Application of the Data Set
  13. Future Modifications and Plans
  14. Software
  15. Data Access
  16. Output Products and Availability
  17. References
  18. Glossary of Terms
  19. List of Acronyms
  20. Document Information

1. Data Set Overview:

Data Set Identification:

LAI & PAR Data: Light Bar - UNL (FIFE).
(Leaf Area Index and PAR Determined from UNL Light Bar Measurements).

Data Set Introduction:

The Leaf Area Index and PAR Determined from UNL Light Bar Measurements Data Set contains total, diffuse, transmitted, reflected, absorbed and intercepted PAR and LAI values. The incoming, reflected, and transmitted photosynthetically active radiation (PAR) were measured with a LI-COR line quantum sensor. The absorbed and intercepted PAR were calculated from these measurements

Objective/Purpose:

The objectives of this research were as follows:

  1. Characterize bi-directional reflectance factor distributions in the solar principal plane for a tall grass prairie.
  2. Estimate surface albedo from bi-directional reflectance factor and radiance data.
  3. Determine the variability of reflected and emitted fluxes in selected spectral wavebands as a function of topography, vegetative community and management practice.
  4. Determine the influence of plant water status on surface reflectance factors.
  5. Determine sun angle affects on radiation fluxes.

Summary of Parameters:

Total, diffuse, transmitted, reflected, absorbed and intercepted PAR and LAI.

Discussion:

Incoming, reflected, and transmitted photosynthetically active radiation (PAR) were measured with a LI-COR LI-191SA line quantum sensor. Absorbed and intercepted PAR were calculated from the above measurements.

The LI-COR LI-191SA line quantum sensor was hand-held in a horizontal position. Incoming (sensor held upright above the canopy surface), reflected (sensor held inverted above the canopy surface), and transmitted (sensor held upright within the canopy) photosynthetically active radiation (PAR) were measured.

1987:

A spatial sampling at a variety of sites as well as within each site was achieved. A number of plots were identified at each site varying from 8-48 depending on the site.

The LI-COR LI-190 SA quantum sensor was mounted on a horizontally held platform. A movable shadow band mounted on the same platform was alternately positioned over and away from the sensor to cast a shadow on the sensor for a diffuse incoming photosynthetically active radiation (PAR) measurement and to measure the total incoming PAR, respectively.

1988:

A spatial and temporal sampling at site 811 (4439-LBN) was achieved.

Four (4) plots were identified at the site.

The LI-COR LI-190 SA quantum sensor was mounted on a horizontally held platform. A movable shadow band mounted on the same platform was alternately positioned over and away from the sensor to cast a shadow on the sensor for a diffuse incoming photosynthetically active radiation (PAR) measurement and to measure the total incoming PAR, respectively.

1989:

A spatial and temporal sampling at sites 906 (2133-LBN) and 916 (4439-LBN) was achieved. Six (6) plots were identified. One of the 6 plots was a bare soil plot prepared with a weed trimmer that removed the surface vegetation with minimal disturbance to the soil surface which left the plant root systems intact. On days when measurements were not made the bare soil was covered with a plastic mulch that allowed moisture to penetrate the surface but hindered the regrowth of vegetation. Measurements were typically coordinated with aircraft and/or satellite overpasses.

Related Data Sets:

FIS Data Base Table Name:

LIGHT_BAR_UNL_DATA.

2. Investigator(s):

Investigator(s) Name and Title:

Blaine L. Blad, Professor and Head
Elizabeth A. Walter-Shea, Asst. Professor
University of Nebraska

Title of Investigation:

Measuring and Modeling Near-Surface Reflected and Emitted Radiation Fluxes at the FIFE Site.

Contact Information:

Contact 1:
Cynthia J. Hays
Lincoln, NE
(402)472-6701

Contact 2:
Mark A. Mesarch
Lincoln, NE
(402)472-5904
AGME012@129.93.200.1

Contact 3:
Elizabeth A. Walter-Shea
Lincoln, NE
(402)472-1553
AGME012@129.93.200.1

Requested Form of Acknowledgment.

The Leaf Area Index and PAR Determined from the UNL Light Bar Data were collected under the direction of B.L. Blad and E.A. Walter-Shea at the University of Nebraska. The dedicated efforts of C.J. Hays and M.A. Mesarch in the collection and preparation of these data is particularly appreciated.

3. Theory of Measurements:

The instantaneous fraction of intercepted direct beam photosynthetically active radiation (IPAR) by a canopy can be described mathematically as:

fIPAR = 1 - exp (-kLAI / cos(zen))

The extinction coefficient, k, is a function of leaf angle distribution and illumination angle. The factor LAI/cos(zen) is the leaf area index divided by the cosine of the solar zenith angle and represents the optical thickness the beam must travel through the vegetation. Thus, the proportion of incident photosynthetically active radiation (PAR) that is intercepted will depend primarily on the canopy structure (LAI and leaf angle distribution) (Russell et al., 1989).

The fraction of PAR absorbed by a canopy (fAPAR) is closely correlated with biomass (Russell et al., 1989). fAPAR is related to fIPAR by the following equation:

fIPAR = (Kdwn - Ktran) / Kdwn

fAPAR = IPAR * [1 - (Krefl / Kdwn)]

where Kdwn is the total incoming PAR above the canopy, Krefl is PAR reflected from the canopy and Ktran is PAR transmitted through the canopy. The equation for fAPAR assumes that PAR reflected from the background back into the canopy is negligible.

4. Equipment:

Sensor/Instrument Description:

The LI-COR LI-191SA line quantum sensor measures photosynthetically active radiation (PAR) in the 0.4 to 0.7 micron waveband and produces an analog voltage response proportional to the scene irradiance. The sensor spatially averages irradiation over its 1 meter length. The sensor size is 116 cm x 2.54 cm x 2.54 cm and weighs 1.8 kg. The serial number of the sensor used is LQA627.

The LI-COR LI-190 SA Quantum sensor measures photosynthetically active radiation (PAR) in the 0.4 to 0.7 micron waveband and produces an analog voltage response proportional to the scene irradiance. In 1987 and 1988 SN Q7434 was used. In 1989 no quantum sensor was used.

Collection Environment:

Ground-based.

Source/Platform:

The LI-COR LI-191 SA line quantum sensor was hand-held in a horizontal position.

The LI-COR LI-190 SA quantum sensor was mounted on platform that was hand-held in a horizontal position. A movable shadow band was mounted on the same platform for measurements of total and diffuse PAR.

Source/Platform Mission Objectives:

Not applicable.

Key Variables:

Incoming, reflected, and transmitted photosynthetically active radiation (PAR) was measured with a LI-COR LI-191SA line quantum sensor. Absorbed and intercepted PAR calculated from the above measurements.

Principles of Operation:

The LI-COR LI-191SA line quantum sensor is comprised of a silicon photodiode with an enhanced response in the visible wave length. The sensor spatially averages irradiation over its 1 meter length. For further information see the LI-COR radiation sensors instruction manual.

The LI-COR LI-190 SA quantum sensor is comprised of a silicon photodiode with an enhanced response in the visible wavelength.

A visible bandpass interference filter and colored glass filter are mounted in a cosine corrected head. For further information see the LI-COR radiation sensors instruction manual.

Sensor/Instrument Measurement Geometry:

The LI-COR LI-191SA line quantum sensor was hand-held in a horizontal position. Incoming photosynthetically active radiation (PAR) were measured with the sensor held upright above the canopy at an approximate height of 1.5 m above the soil surface. Reflected PAR were measured with the sensor held inverted above the canopy at an approximate height of 0.5 m above the canopy surface. Transmitted PAR were measured with the sensor held upright in the canopy at the soil surface. The sensor has a near hemispherical field-of-view along its 1 m length.

The LI-COR 190 SA quantum sensor was mounted on a platform with a movable shadow band. The platform was hand-held in a horizontal position at an approximate height of 1.25 m above the soil surface. The shadow band was alternatively positioned over and away form the sensor for measurements of incoming diffuse and total PAR. The sensor has a near hemispherical field-of-view.

Manufacturer of Sensor/Instrument:

LI-COR, inc.
4421 Superior Street
P.O. Box 4425
Lincoln, Nebraska 68504
(402) 467-3576

Calibration:

LI-COR 191SA line quantum sensor was calibrated by LI-COR on May 1, 1987.

LI-COR 190 SA quantum sensor was calibrated by LI-COR before May 1987.

Specifications:

The LI-COR LI-191SA line quantum sensor measurements are used to estimate the fraction of absorbed and intercepted photosynthetically active radiation (PAR). Since the reflected and transmitted PAR measurements are normalized to the total incoming PAR during the calculation of absorbed and intercepted PAR, accurate measurements of PAR are not necessary, then relative measurements of PAR can be used and frequent calibrations are not required.

The LI-COR LI-190 SA quantum sensor measurements are used to estimate the fraction of direct beam photosynthetically active radiation. Since this measurement of direct PAR is normalized to the incoming PAR, accurate measurements of PAR are not necessary, then relative measurements of PAR can be used and frequent calibrations are not required.

The sensor surfaces of the LI-191SA and LI-190 SA should be cleaned periodically so that responses are always comparable.

Tolerance:

The LI-COR 190 SA Quantum sensor absolute calibration is within +/- 5% (usually with +/- 3% under most sky conditions. It is cosine corrected up to an 80 degree solar zenith angle.

The LI-COR LI-191SA line quantum sensor absolute calibration is within +/- 10%. The cosine error is less then 10% for solar zenith angles less then 60 degrees. The response uniformity along the 1 meter sensing length varies less then +/- 7%.

Frequency of Calibration:

Not applicable (See the Specifications Section).

Other Calibration Information:

LI-COR LI-191SA line quantum sensor.
147.32 [microEinstein][sec^-1][m^-2][mv^-1] (LI-COR calibration May 1, 1987).

LI-COR LI-190 SA quantum sensor.
229.1055 [microEinstein][sec^-1][m^-2][mv^-1] (LI-COR calibration).

5. Data Acquisition Methods:

1987:

Measurements were not made in coincident with any other measurements.

Measurements were taken once per day at a particular site.

The LI-COR LI-191SA line quantum sensor was hand-held. The LI-COR LI-190 SA quantum sensor and movable shadow band were also mounted on a platform that was hand-held. Both sensors were leveled (horizontal position) before a measurement was made. Both sensors were aligned in the solar principal plane, with the sensor between the observer and the sun (i.e., the observer facing the sun). The quantum sensor was held at an approximate height of 1.25 m above the soil surface for all measurements. Four measurements from each sensor were made at a location within each plot:

  1. the line quantum held upright above the canopy at an approximate height of 1.5 m above the soil surface, the movable shadow band was positioned so that the quantum sensor was not shadowed,
  2. The line quantum sensor was held inverted above the canopy at an approximate height of 0.5 m above the canopy surface, the movable shadow band was positioned to shadow the quantum sensor,
  3. The line quantum sensor was held upright in the canopy at the soil surface, the movable shadow band was positioned so that the quantum sensor was not shadowed, and
  4. The line quantum was held upright above the canopy at an approximate height of 1.5 m above the soil surface, the movable shadow band was positioned so that the quantum sensor was not shadowed.

The 4 measurements described above were made 1 - 14 times at each plot.

A plot number larger then 60 signifies that data was taken near a neutron tube at that site.

1988:

Three replications of the four measurements were made at each plot. The shadow band was always moved just to the side when not shadowing the sensor. Unless otherwise noted the same procedure as in 1987 was followed.

1989:

Measurements were made in coincident with other ground measurements throughout the day. The LI-COR LI-190 SA quantum sensor was not used. Only one replication of the 4 measurements were made at each plot. Plot 6 is near the PARABOLA measurement area. Unless otherwise noted the same procedure as in 1987 was followed.

6. Observations:

Data Notes:

Not available.

Field Notes:

1987: None.

1988: None.

1989:

  • July 26 Site 916(4439-LBN) Few clouds on horizon, measurement periods: 1455-1500 GMT.
  • July 28 Site 916(4439-LBN) Clear skies except for cumulus during last measurement period, measurement periods: 1430-1436, 1539-1545, 1647-16150 1717-1722 GMT.
  • Aug. 4 Site 916(4439-LBN) Clear skies, measurement periods: 1501-1508, 1750-1758, 2004-2010 GMT.
  • Aug. 6 Site 906(2133-LBN) Clear skies measurement periods: 1507-1512, 1630-1635, 1846-1851, 1959-2006 and 2111-2117 GMT.
  • Aug. 7 Site 906(2133-LBN) Cumulus during first measurement period, the clear skies, measurement periods: 1759-1804 and 1913 GMT.
  • Aug. 8 Site 916(4439-LBN) Clear skies, measurement periods: 1425-1441, 1446-1407, 1625-1643 2033-2043 and 2124-2138 GMT.
  • Aug. 10 Site 906(2133-LBN) Possible cirrus clouds, measurement period: 1538-1559 GMT.
  • 7. Data Description:

    Spatial Characteristics:

    The FIFE study area, with areal extent of 15 km by 15 km, is located south of the Tuttle Reservoir and Kansas River, and about 10 km from Manhattan, Kansas, USA. The northwest corner of the area has UTM coordinates of 4,334,000 Northing and 705,000 Easting in UTM Zone 14.

    Spatial Coverage:

    In 1987 and 1988 measurement plots generally encircled the AMS station located at that site. In 1989 measurements plots were located northeast of the Wind Aligned Blob (WAB) site (Sellers et al., 1989). Topography files containing the northing and easting of the plots at each site, except for site 18 (SITEGRID_ID = 4439-LBN) and 170 (SITEGRID_ID = 0939-LBN) in 1987 and site 966 (SITEGRID_ID = 2437-LBN) in 1989, are available in the GRAB-BAG section of FIFE CD-ROM Volume 1 in the UNL directory, in files UNL_PLOT.T87, UNL_PLOT.T88, UNL_PLOT.T89. These files also include the slope, aspect, soil depth, species and vegetative height of the plots.

    Data were collected from 13 stations as listed below, in 11 different sitegrids. The stations were scattered throughout the FIFE study area but the northwest quadrant had the highest number of stations.

          SITEGRID   STN_ID   NORTHING   EASTING   LATITUDE    LONGITUDE    ELEV
    --------   ------   --------   -------   --------    ---------    -----
    0847-LBN      29    4332344    714439    39 06 57    -96 31 11    418
    1246-LBN      40    4331666    714212    39 06 35    -96 31 21    365
    1445-LBN      42    4331160    714090    39 06 19    -96 31 27    400
    1916-LBN      70    4330296    708263    39 05 56    -96 35 30    340
    2123-LBN       5    4329866    709506    39 05 41    -96 34 39    405
    2133-LBN     906    4329726    711604    39 05 34    -96 33 12    443
    3414-LBN      10    4327286    707854    39 04 19    -96 35 51    410
    4268-LBN      32    4325626    718579    39 03 15    -96 28 27    445
    4439-LBN      18    4325218    712792    39 03 07    -96 32 28    445
    4439-LBN     916    4325193    712773    39 03 06    -96 32 28    443
    4439-LBN     811    4325219    712795    39 03 07    -96 32 27    445
    6943-LBN      28    4320147    713500    39 00 22    -96 32 04    415
    8739-LBN      26    4316699    712845    38 58 31    -96 32 35    442
          SITEGRID    SLOPE   ASPECT
    --------    -----   ------
    0847-LBN      1      TOP
    1246-LBN
    1445-LBN
    1916-LBN
    2123-LBN
    2133-LBN      1      TOP
    3414-LBN
    4268-LBN
    4439-LBN
    4439-LBN      2      N  
    4439-LBN      2      N
    6943-LBN
    8739-LBN
    

    Spatial Coverage Map:

    Not available.

    Spatial Resolution:

    The LI-COR LI-191SA line quantum sensor and LI-COR LI-190 SA quantum sensor have a near hemispherical field-of-view. The plot size was approximately 3 m x 3 m. At each site 8 to 48 plots were measured.

    Projection:

    Not available.

    Grid Description:

    Not available.

    Temporal Characteristics:

    The time required for a measurement at a plot depended on the number of replications made at each plot. One set of four measurements took approximately 1 minute. The time (5 to 60 minutes) to complete all the measurements at a site depended on the number of replications at each plot and the number of plots.

    In 1989 measurements were usually coordinated with aircraft and satellite overpasses.

    Temporal Coverage:

    The measurement time ranged from 1155 to 2136 GMT. Measurements were not continuously made over this range but were in discrete measurement periods.

    In 1987 and 1988 only one discrete measurement period per day was obtained at the sites measured.

    In 1989 data were obtained at only one site per day. A maximum of five (5) discrete measurement periods throughout the day were obtained.

    Temporal Coverage Map:

    Not available.

    Temporal Resolution:

    The optimum time interval between plot measurements was approximately 1-2 minutes. The typical time interval between plots was approximately 5 minutes. The time interval depended on the distance between the plots, the terrain, and sky conditions.

    Data Characteristics:

    The SQL definition for this table is found in the LB_UNL.TDF file located on FIFE CD-ROM Volume 1.


    Parameter/Variable Name
    Parameter/Variable Description Range Units Source
    SITEGRID_ID This is a FIS grid location code. Site grid codes (SSEE-III) give the south (SS) and east (EE) cell number in a 100 x 100 array of 200 m square cells. The last 3 characters (III) are an instrument identifier.
    STATION_ID The station ID designating the location of the observations.
    OBS_DATE The date of the observations, in the format (DD-MMM-YY).
    OBS_TIME The time that the observation was [GMT] taken in GMT. The format is (HHMM).
    PLOT_NUM The Nebraska Plot Number, taken from the Nebraska topography file. A plot number with an F means the shadow band on the quantum sensor was far away, not off to the side.
    QUANTM_TOT_INCOM_PAR The Quantum Total Incoming PAR [microEinst] (Photosynthetically active [meter^-2] radiation) [Abbreviated QT]. [sec^-1]
    QUANTM_DIFUS_INCOM_PAR The Quantum Diffuse Incoming PAR [microEinst] (Photosynthetically active [meter^-2] radiation) [Abbreviated QD]. [sec^-1]
    LINE_QUANTM_TOT_INCOM_PAR The Line Quantum Total Incoming [microEinst] PAR (Photosynthetically active [meter^-2] radiation) [Abbreviated LT]. [sec^-1]
    LINE_QUANTM_TRNS_PAR The Line Quantum PAR [microEinst] (Photosynthetically active [meter^-2] radiation) transmitted through the [sec^-1] canopy [Abbreviated LC].
    LINE_QUANTM_REFL_PAR The Line Quantum Reflected PAR [microEinst] (Photosynthetically active [meter^-2] radiation) [Abbreviated LR]. [sec^-1]
    INDIRECT_LAI The Indirect LAI; FB=(QT-QD)/QT,
    FRACTION_ABSORB_PAR The fraction of absorbed PAR (Photosynthetically active radiation), determined by IPAR x (1-(LR/LT)).
    FRACTION_INTERCEPT_PAR The fraction of intercepted PAR (Photosynthetically active radiation), determined by (LT-LC)/LT.
    SOLAR_ZEN_ANG The solar zenith angle. [degrees]
    SOLAR_AZIM_ANG The solar azimuth angle. [degrees from North]
    FIFE_DATA_CRTFCN_CODE The FIFE Certification Code for * the data, in the following format: CPI (Certified by PI), CPI-??? (CPI - questionable data).
    LAST_REVISION_DATE data, in the format (DD-MMM-YY).

    Footnote:

    Valid levels

    The primary certification codes are: EXM Example or Test data (not for release) PRE Preliminary (unchecked, use at your own risk) CPI Checked by Principal Investigator (reviewed for quality) CGR Checked by a group and reconciled (data comparisons and cross checks)

    The certification code modifiers are: PRE-NFP Preliminary - Not for publication, at the request of investigator. CPI-MRG PAMS data that is "merged" from two separate receiving stations to eliminate transmission errors. CPI-??? Investigator thinks data item may be questionable.

    Sample Data Record:

         SITEGRID_ID  STATION_ID  OBS_DATE    OBS_TIME  PLOT_NUM   QUANTM_TOT_INCOM_PAR
    -----------  ----------  ----------  --------  --------   --------------------
    1246-LBN         40      12-OCT-87     1652       8              1656.0
    4439-LBN         18      13-OCT-87     1839      10               986.4
    4439-LBN         18      13-OCT-87     1840      10               969.6
    4439-LBN         18      13-OCT-87     1841      10               969.5
         QUANTM_DIFUS_INCOM_PAR   LINE_QUANTM_TOT_INCOM_PAR   LINE_QUANTM_TRNS_PAR
    ----------------------   -------------------------   --------------------
    250.6                     986.7                    689.6
    647.7                     723.4                     93.4
    638.8                     706.6                    115.2
    645.9                     678.6                     65.9
         LINE_QUANTM_REFL_PAR   INDIRECT_LAI   FRACTION_ABSORB_PAR
    --------------------   ------------   -------------------
    82.2              .583              .276
    67.9             3.030              .789
    69.6             2.683              .754
    68.7             3.443              .812
         FRACTION_INTERCEPT_PAR   SOLAR_ZEN_ANG   SOLAR_AZIM_ANG   FIFE_DATA_CRTFCN_CODE
    ----------------------   -------------   --------------   ---------------------
    .301               49.212          152.857                 CPI
    .871               46.177          188.910                 CPI
    .837               46.208          189.251                 CPI
    .903               46.240          189.592                 CPI
         LAST_REVISION_DATE
    ------------------
    28-JUN-89
    28-JUN-89
    28-JUN-89
    28-JUN-89
    

    8. Data Organization:

    Data Granularity:

    Data were collected from 13 stations, in 11 different sitegrids. At each site 8 to 48 plots were measured. The data collected includes slope, aspect, soil depth, species and vegetative height of the plots.

    A general description of data granularity as it applies to the IMS appears in the EOSDIS Glossary.

    Data Format:

    The CD-ROM file format consists of numerical and character fields of varying length separated by commas. The character fields are enclosed with a single apostrophe. There are no spaces between the fields. Each file begins with five header records. Header records contain the following information: Record 1 Name of this file, its table name, number of records in this file, path and name of the document that describes the data in this file, and name of principal investigator for these data. Record 2 Path and filename of the previous data set, and path and filename of the next data set. (Path and filenames for files that contain another set of data taken at the same site on the same day.) Record 3 Path and filename of the previous site, and path and filename of the next site. (Path and filenames for files of the same data set taken on the same day for the previous and next sites (sequentially numbered by SITEGRID_ID)). Record 4 Path and filename of the previous date, and path and filename of the next date. (Path and filenames for files of the same data set taken at the same site for the previous and next date.) Record 5 Column names for the data within the file, delimited by commas. Record 6 Data records begin.

    Each field represents one of the attributes listed in the chart in the Data Characteristics Section and described in detail in the TDF file. These fields are in the same order as in the chart.

    9. Data Manipulations:

    Formulae:

    K = V * CC [1]

    where:

    K = photosynthetically active radiation [microEinstein][sec^-1][m^-2]
    V = voltage (mV)
    CC = calibration coefficient [microEinstein][sec^-1][m^-2][mV^-1]

    Kldwn = [Kldwn(1) + Kldwn(2)] / 2 [2]

    where:

    Kldwn (1 or 2) = incoming photosynthetically active radiation taken before and after the transmitted and reflected measurements made with the LI-191SA line quantum sensor [microEinstein][sec^-1][m^-2]
    Kldwn = average incoming photosynthetically active radiation measured with the LI-191SA line quantum sensor [microEinstein][sec^-1][m^-2]

    fIPAR = (Kldwn-Ktran) / Kldwn [3]

    where:

    fIPAR = fraction of intercepted photosynthetically active radiation (unitless)
    Kldwn = average incoming photosynthetically active radiation measured with the LI-191SA line quantum sensor [microEinstein][sec^-1][m^-2]
    Ktran = transmitted photosynthetically active radiation through the canopy measured with the LI-191SA line quantum sensor [microEinstein][sec^-1][m^-2]

    fAPAR = (fIPAR * [ 1 - (Krefl / Kldwn)] [4]

    where:

    fAPAR = fraction of absorbed photosynthetically active radiation (unitless)
    fIPAR = fraction of intercepted photosynthetically active radiation (unitless)
    Kldwn = average incoming photosynthetically active radiation measured with the LI-191SA line quantum sensor [microEinstein][sec^-1][m^-2]
    Krefl = reflected photosynthetically active radiation measured with the LI-191SA line quantum sensor [microEinstein][sec^-1][m^-2]

    Kdwn = [Kdwn(1) + Kdwn(2) + Kdwn(3)] / 3 [5]

    where:

    Kdwn = average incoming photosynthetically active radiation measured with the LI-190 SA quantum sensor [microEinstein][sec^-1][m^-2]
    Kdwn (1 or 2 or 3) = incoming photosynthetically active radiation taken before and after the diffuse measurements made with the LI-190 SA quantum sensor [microEinstein][sec^-1][m^-2]

    Kdir = (Kdwn - Kdif) / Kdwn [6]

    where:

    Kdwn = average incoming photosynthetically active radiation measured with the LI-190 SA quantum sensor [microEinstein][sec^-1][m^-2]
    Kdif = diffuse incoming photosynthetically active radiation measured with the LI-190 SA quantum sensor [microEinstein][sec^-1][m^-2]
    Kdir = fraction of direct incoming photosynthetically active radiation (unitless)

    LAI = {[(1 -cos(ZEN)) * Kdir - 1] * ln(Ktran / Kldwn)} / (0.72-0.33 * Kdir) [7]

    where:

    LAI = indirect leaf area index (unitless)
    ZEN = solar zenith angle (degrees)
    Kdir = fraction of direct incoming photosynthetically active radiation (unitless)
    Ktran = transmitted photosynthetically active radiation measured with LI-191SA line quantum sensor [microEinstein][sec^-1][m^-2]
    Kldwn = incoming photosynthetically active radiation measured with the LI-191SA line quantum sensor [microEinstein][sec^-1][m^-2]

    Derivation Techniques and Algorithms:

    Not available at this revision.

    Data Processing Sequence:

    Processing Steps:

    The calibration coefficients used are listed in the Other Calibration Information Section.

    1987, 1988 and 1989:

    Equation 1 is used to convert the LI-COR LI-191SA line quantum sensor voltages to incoming, reflected and transmitted photosynthetically active radiation (PAR) [microEinstein][sec^-1][m^-2]. Equation 2 is used to calculate the average incoming PAR from the two measurements bracketing the reflected and transmitted PAR measurements with the LI-191SA line quantum sensor. Equation 3 is then used to calculate the fraction of intercepted PAR. The fraction of intercepted PAR is then used in equation 4 to calculate the fraction of absorbed PAR.

    1987 and 1988:

    Equation 1 is used to convert the LI-COR LI-190 SA quantum sensor voltages to total and diffuse incoming photosynthetically active radiation (PAR) [microEinstein][sec^-1][m^-2]. Equation 5 is used to calculate the averaging total incoming PAR from the measurements bracketing the diffuse incoming PAR made with the LI-190 SA quantum sensor. Equation 6 is used to calculate the fraction of direct beam. Equation 7 is then used to calculate the indirect leaf area index (Norman 1987).

    Processing Changes:

    Not available at this revision.

    Calculations:

    Special Corrections/Adjustments:

    Not available at this revision.

    Calculated Variables:

    Graphs and Plots:

    None.

    10. Errors:

    Sources of Error:

    Variable cloud cover could be an error source if comparing measurements from the various plots within a measurement period.

    The soil surface reflectance was not included in the calculation of the fraction of absorbed photosynthetically active radiation (fAPAR), this could result in an under estimation of fAPAR.

    Quality Assessment:

    Data Validation by Source:

    Leaf area index values were compared with values obtained from different methods and values from other investigators (Kim et al., 1989).

    Confidence Level/Accuracy Judgment:

    ABSORBED AND INTERCEPTED PHOTOSYNTHETICALLY ACTIVE RADIATION

    On days with variable cloud conditions the data should be used with caution. The AMS incoming solar radiation data at the site or nearby site should be consulted. On clear days the measurements fall within the precision of the instrument and errors that were discussed in previous sections. The equation used to calculate fAPAR is not the standard equation for the calculation of fAPAR. This equation assumes that PAR reflected from the background, back into the canopy is negligible.

    LEAF AREA INDEX

    Always overestimates leaf area index since this measurement is actually a foliage area index and measures leaves and stems and does not distinguish between green and dead foliage. Comparisons with the LAI-2000 usually showed good agreement in 1988 through out the season. Comparisons with destructive leaf area index measurements agreements were good when leaf area indexes were under 3 and early in the season. Destructive leaf area indexes were lower later in the season, this could be due to the greater number of senescence leaves that were not included in the destructive leaf area index. There can be considerable variability in leaf area index values, especially in natural ecosystems such as that found at the FIFE study area. Therefore, some of the differences between leaf area index values observed using the different approaches can surely be attributed to this natural variability (Kim et al., 1989).

    Measurement Error for Parameters:

    Not available at this revision.

    Additional Quality Assessments:

    FIS staff applied a general QA procedure to the data to identify inconsistencies and problems for potential users. As a general procedure, the FIS QA consisted of examining the maximum, minimum, average, and standard deviation for each numerical field in the data table. In some cases, histograms were examined to determine whether outliers were consistent with the shape of the data distribution. Inconsistencies and problems found in the QA check are described is the Known Problems with the Data Section.

    Data Verification by Data Center:

    The data verification performed by the ORNL DAAC deals with the quality of the data format, media, and readability. The ORNL DAAC does not make an assessment of the quality of the data itself except during the course of performing other QA procedures as described below.

    The FIFE data were transferred to the ORNL DAAC via CD-ROM. These CD-ROMs are distributed by the ORNL DAAC unmodified as a set or in individual volumes, as requested. In addition, the DAAC has incorporated each of the 98 FIFE tabular datasets from the CD-ROMs into its online data holdings. Incorporation of these data involved the following steps:

    Each distinct type of data (i.e. "data set" on the CD-ROM), is accompanied by a documentation file (i.e., .doc file) and a data format/structure definition file (i.e., .tdf file). The data format files on the CD-ROM are Oracle SQL commands (e.g., "create table") that can be used to set up a relational database table structure. This file provides column/variable names, character/numeric type, length, and format, and labels/comments. These SQL commands were converted to SAS code and were used to create SAS data sets and subsequently to input data files directly from the CD-ROM into a SAS dataset. During this process, file names and directory paths were captured and metadata was extracted to the extent possible electronically. No files were found to be corrupted or unreadable during the conversion process.

    Additional Quality Assurance procedures were performed as follows:

    As errors are discovered in the online tabular data by investigators, users, or DAAC staff, corrections are made in cooperation with the principal investigators. These corrections are then distributed to users. CD-ROM data are corrected when re-mastering occurs for replenishment of CD-ROM stock.

    11. Notes:

    Limitations of the Data:

    Not available.

    Known Problems with the Data:

    As of the revision data of this document, the following discrepancies or errors in the data have been reported:

  • July 20, 1987 observation time of 1539 GMT should be July 23, 1987 observation time of 1539 GMT.
  • Results of the FIS staff quality assessments:

  • Solar Azimuth Angle readings go from 70 - 250. All readings less than 90 are before 1430 GMT.
  • Negative values occurred with indirect LAI on two occasions, for fAPAR on eight occasions, and for fIPAR on eight occasions.
  • Usage Guidance:

    Before using these data the incoming radiation from the AMS station at the site or nearby site should be checked for possible cloud-induced errors.

    Any Other Relevant Information about the Study:

    Not available at this revision.

    12. Application of the Data Set:

    This data set can be utilized to help characterize bi-directional reflectance factor distributions in the solar principal plane for a tall grass prairie, estimate surface albedo from bi-directional reflectance factor and radiance data, determine the variability of reflected and emitted fluxes in selected spectral wavebands as a function of topography, vegetative community and management practice, determine the influence of plant water status on surface reflectance factors, and determine sun angle affects on radiation fluxes.

    13. Future Modifications and Plans:

    The FIFE field campaigns were held in 1987 and 1989 and there are no plans for new data collection. Field work continues near the FIFE site at the Long-Term Ecological Research (LTER) Network Konza research site (i.e., LTER continues to monitor the site). The FIFE investigators are continuing to analyze and model the data from the field campaigns to produce new data products.

    14. Software:

    Software to access the data set is available on the all volumes of the FIFE CD-ROM set. For a detailed description of the available software see the Software Description Document.

    15. Data Access:

    Contact Information:

    ORNL DAAC User Services
    Oak Ridge National Laboratory

    Telephone: (865) 241-3952
    FAX: (865) 574-4665

    Email: ornldaac@ornl.gov

    Data Center Identification:

    ORNL Distributed Active Archive Center
    Oak Ridge National Laboratory
    USA

    Telephone: (865) 241-3952
    FAX: (865) 574-4665

    Email: ornldaac@ornl.gov

    Procedures for Obtaining Data:

    Users may place requests by telephone, electronic mail, or FAX. Data is also available via the World Wide Web at http://daac.ornl.gov.

    Data Center Status/Plans:

    FIFE data are available from the ORNL DAAC. Please contact the ORNL DAAC User Services Office for the most current information about these data.

    16. Output Products and Availability:

    Leaf Area Index and PAR Determined from UNL Light Bar Measurements are available on FIFE CD-ROM Volume 1. The CD-ROM file name is as follows:

    \DATA\SUR_RELF\LTBR_UNL\GRIDxxxx\ydddgrid.LBU

    Where xxxx is the four digit code for the location within the FIFE sitegrid. Note: capital letters indicate fixed values that appear on the CD-ROM exactly as shown here, lower case indicates characters (values) that change for each path and file.

    The format used for the filenames is: ydddgrid.sfx, where grid is the four-number code for the location within the FIFE sitegrid, y is the last digit of the year (e.g., 7 = 1987, 9 = 1989), and ddd is the day of the year (e.g., 061 = sixty-first day of the year). The filename extension (.sfx), identifies the data set content for the file (see the Data Characteristics Section) and is equal to .LBU for this data set.

    17. References:

    Satellite/Instrument/Data Processing Documentation.

    LI-COR Terrestrial Radiation Sensors, Type SA Instruction Manual.
    LI-COR, inc. Lincoln, NE (1986).

    Journal Articles and Study Reports.

    Kim, J., C. Hays, S. Verma, B. Blad. 1989. A preliminary Report on LAI values obtained during FIFE by various methods. Department of Agricultural Meteorology. University of Nebraska-Lincoln. Lincoln, NE 68583-0728.

    Norman, J.M. 1987. Personal communication. University of Wisconsin. Madison, WI 53706.

    Russell, G., P.G. Jarvis, and J.L. Monteith. 1989. Absorption of radiation by canopies and stand growth, in Plant Canopies: Their Growth, Form and Function. edited by G. Russell, B. Marshall and P.G. Jarvis. pp. 21-39. Cambridge University Press, New York.

    Archive/DBMS Usage Documentation.

    Contact the EOS Distributed Active Archive Center (DAAC) at Oak Ridge National Laboratory (ORNL), Oak Ridge, Tennessee (see the Data Center Identification Section). Documentation about using the archive and/or online access to the data at the ORNL DAAC is not available at this revision.

    18. Glossary of Terms:

    A general glossary for the DAAC is located at Glossary.

    19. List of Acronyms:

    APAR Absorbed Photosynthetically Active Radiation DAAC Distributed Active Archive Center EOSDIS Earth Observing System Data and Information System FIFE First ISLSCP Field Experiment FIS FIFE Information System fAPAR Fraction of Absorbed Photosynthetically Active Radiation fIPAR Fraction of Intercepted Photosynthetically Active Radiation IPAR Intercepted Photosynthetically Active Radiation IRT Infrared Thermometer ISLSCP Intention Satellite Land Surface Climatology Project KSU Kansas State University LAI Leaf Area Index MMR Modular Multiband Radiometer ORNL Oak Ridge National Laboratory PAR Photosynthetically Active Radiation UNL University of Nebraska - Lincoln URL Uniform Resource Locator UTM Universal Transverse Mercator WAB Wind Aligned Blob

    A general list of acronyms for the DAAC is available at Acronyms.

    20. Document Information:

    April 24, 1994 (citation revised on October 16, 2002).

    Warning: This document has not been checked for technical or editorial accuracy by the FIFE Information Scientist. There may be inconsistencies with other documents, technical or editorial errors that were inadvertently introduced when the document was compiled or references to preliminary data that were not included on the final CD-ROM.

    Previous versions of this document have been reviewed by the Principal Investigator, the person who transmitted the data to FIS, a FIS staff member, or a FIFE scientist generally familiar with the data.

    Document Review Date:

    July 23, 1996.

    Document ID:

    ORNL-FIFE_LB_UNL.

    Citation:

    Cite this data set as follows:

    Blad, B. L., and E. A. Walter-Shea. 1994. LAI and PAR Data: Light Bar - UNL (FIFE). Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. doi:10.3334/ORNLDAAC/42. Also published in D. E. Strebel, D. R. Landis, K. F. Huemmrich, and B. W. Meeson (eds.), Collected Data of the First ISLSCP Field Experiment, Vol. 1: Surface Observations and Non-Image Data Sets. CD-ROM. National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, Maryland, U.S.A. (available from http://www.daac.ornl.gov).

    Document Curator:

    DAAC Staff

    Document URL:

    http://daac.ornl.gov