Summary:

This Albedo and BRDF (Bidirectional Reflectance Distribution Function) data set consists of three files containing BRDF parameters, white- sky albedo and black-sky albedo at solar noon for three bands ((350-680nm, 680-3000nm, and 350-30000nm) derived from AVHRR (Advanced Very High Resolution Radiometer). These data are available at spatial resolutions of quarter, half, and one degree. Black-sky albedo (direct beam contribution) and white-sky (Completely diffuse contribution) can be linearly combined as a function of the fraction of diffuse skylight (itself a function of optical depth) to provide an actual or instantaneous albedo at local solar noon.

Additional Documentation:

This data set is one of the products of the International Satellite Land-Surface Climatology Project, Initative II (ISLSCP II) data collection which contains 50 global time series data sets for the ten-year peroid 1986 to 1995. A complete description of the data, their derivation, acknowledgements, and references provided by the ISLSCP II Data Management Staff is included with this data set as a companion file named 1_avhrr_albedo_1995_doc.pdf.

ISLSCP II is a consistent collection of data sets that were compiled from existing data sources and algorithms, and were designed to satisfy the needs of modelers and investigators of the global carbon, water and energy cycle. The data were acquired from a number of U.S. and international agencies, universities, and institutions, and have undergone two peer reviews.

ISLSCP is one of several projects of Global Energy and Water Cycle Experiment (GEWEX) [http://www.gewex.org/] and has the lead role in addressing land-atmosphere interactions -- process modeling, data retrieval algorithms, field experiment design and execution, and the development of global data sets.

Data Citation:

Cite this data set as follows:

Strahler, A.H., C.L.B. Schaaf, and E. Tsvetsinskaya. 2009. ISLSCP II AVHRR Albedo and BRDF, 1995. In Hall, Forrest G., G. Collatz, B. Meeson, S. Los, E. Brown de Colstoun, and D. Landis (eds.). ISLSCP Initiative II Collection. Data set. Available on-line [http://daac.ornl.gov/] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. doi:10.3334/ORNLDAAC/928

Data Description:

The archived data sets for ISLSCP II have been organized by categories. This data set is in the vegetation category--a collection of vegetation and albedo data sets.

Data Set Spatial Extent: Global gridded

Western most Longitude: -180 W

Easternmost Longitude: 180 E

Northernmost Latitude: 90N

Southernmost Latitude: -90S

Projection: Geographic

Data Set Spatial Resolution: 1/4, 1/2, and 1 degrees in both latitude and longitude

Data Set Temporal Extent: February through July in 1995

Data Set Temporal Resolution: Synoptic months February and July in 1995

Data File Format:

All of the data files in each data set within the ISLSCP Initiative II data collection are in ESRI ASCII GRID format for ArcInfo. All files are gridded to a common equal-angle lat/long grid. The data files are grouped by spatial resolution and each file has 6 header metadata rows.

avhrr_albedo_1degree_1995.zip: ncols360, nrows180, xllcorner-180, yllcorner-90 ,cellsize 1, NODATA_value -99

avhrr_albedo_hdegree_1995.zip: ncols 720, nrows 360, xllcorner-180, yllcorner-90, cellsize.5, NODATA_value -99

avhrr_albedo_qdegree_1995.zip: ncols 1440, nrows 720, xllcorner-180, yllcorner-90, cellsize .25, NODATA_value -99

When the .zip files in this data set are expanded, the result is 30*.asc and 30*.dif pairs of files. There is one ".dif" file for each map file. The files are named for the various AVHRR BRDF model parameters reported and for either the month of February or July in 1995.

The ISLSCP II staff processed the original files by comparing the original data set for consistency against the ISLSCP II land/water mask.

Missing data over land cells in these files were coded with a value of -88.
Grid cells where the data file contained a data value and the ISCLSCP II land/water mask contained water, were removed and replaced with the value of -99.
Files containing the removed points (points that didn't match the land/water mask), called "difference" files with the extension .dif, were created. These files contain the Latitude and Longitude of the cell-center of each removed point and the data value at that point.

Data Values:

All values are written as floating point values.

Missing values are assigned the value of -99 on all data layers.

Missing values over land are assigned the value of -88.

Within each of the *.zip files, the data files fall into the following categories. Data file naming conventions are described in the 0_avhrr_albedo_readme.txt file.

Black Sky Albedo (BSA)	Black-sky albedo derived from AVHRR data from 1995. Albedo is the fraction of incident solar radiation that a surface reflects -- in this case under entirely direct solar illumination conditions.
White Sky Albedo (WSA)	White-sky albedo derived from AVHRR data from 1995. Albedo is the fraction of incident solar radiation that a surface reflects -- in this case under entirely diffuse solar illumination conditions.
BRDF parameters (BRDF)	Three BRDF Model Parameters (isotropic, volumetric and geometric) derived from AVHRR data from 1995.

Data Access:

These data are available through the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC) [http://daac.ornl.gov].

Data Archive Contact Information:

E-mail: uso@daac.ornl.gov
Telephone: +1 (865) 241-3952