BOREAS RSS-16 Level-3b DC-8 AIRSAR SY Images Summary The BOREAS RSS-16 team used satellite and aircraft SAR data in conjunction with various ground measurements to determine the moisture regime of the boreal forest. RSS-16 assisted with the acquisition and ordering of NASA JPL AIRSAR data collected from the NASA DC-8 aircraft. The NASA JPL AIRSAR is a side- looking imaging radar system that utilizes the SAR principle to obtain high resolution images that represent the radar backscatter of the imaged surface at different frequencies and polarizations. The information contained in each pixel of the AIRSAR data represents the radar backscatter for all possible combinations of horizontal and vertical transmit and receive polarizations (i.e., HH, HV, VH, and VV). Geographically, the data cover portions of the BOREAS SSA and NSA. Temporally, the data were acquired from 12-Aug-1993 to 31- Jul-1995. The level-3b AIRSAR SY data are the JPL synoptic product and contain 3 of the 12 total frequency and polarization combinations that are possible. The data are stored in binary image format files. Please note: None of the AIRSAR imagery is contained on the BOREAS CD-ROM. An inventory listing of data collected is included. 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 1.1 Data Set Identification BOREAS RSS-16 Level-3b DC-8 AIRSAR SY Images 1.2 Data Set Introduction The BOReal Ecosystem-Atmosphere Study (BOREAS) Staff Science effort covered those activities that were BOREAS community-level activities or required uniform data collection procedures across sites and time. These activities included the acquisition of the relevant aircraft image data. Data from the Airborne Synthetic Aperture Radar (AIRSAR) system onboard the National Aeronautics and Space Administration (NASA) DC-8 aircraft were acquired by staff at the Jet Propulsion Laboratory (JPL) and provided for use by BOREAS researchers. 1.3 Objective/Purpose The purpose of this data set is to provide multifrequency and multipolarization Synthetic Aperture Radar (SAR) images over the BOREAS Southern Study Area (SSA). This data set supplements other visible and near-infrared remote sensing images compiled by BOREAS. The level-3b AIRSAR data were acquired at three frequencies of P-band, L-band, and C-band and for all linear polarization combinations (HH, HV, VH, and VV). The level-3b AIRSAR SY image data products contain data from 3 frequency and polarization combinations. AIRSAR images are used to estimate surface parameters such as canopy water content, soil moisture, and stand biomass and density. 1.4 Summary of Parameters SAR parameters: incidence angle, aircraft altitude, range resolution, azimuth resolution, frequency, polarization. 1.5 Discussion AIRSAR image data gathering for BOREAS was conducted in 1993 and 1994 over the two study areas in Canada. BOREAS was designed to study regional land surface climatology and to develop methods for deriving quantitative information about surface variables from remote sensing data. The AIRSAR experiment was devised to provide surface moisture and vegetation variables suitable for the soil- vegetation-atmosphere interaction models. In particular, the high-resolution data obtained by the AIRSAR system can be used to derive information about the variability of the surface parameters, which in turn can be used to address the scaling problem. 1.6 Related Data Sets BOREAS RSS-16 Level-3b DC-8 AIRSAR CM Images 2. Investigator(s) 2.1 Investigator(s) Name and Title Dr. Sasan S. Saatchi 2.2 Title of Investigation Estimation of Evapotranspiration Using SAR Derived Parameters 2.3 Contact Information Contact 1 ------------- Dr. Sasan S. Saatchi Jet Propulsion Laboratory Pasadena, CA (818) 354-1051 saatchi@bacchus.jpl.nasa.gov Contact 2 ---------------- Dr. Jakob J. vanZyl Jet Propulsion Laboratory Pasadena, CA (818) 354-1365 Contact 3 ------------- Jeffrey Newcomer Raytheon STX Corporation NASA GSFC Greenbelt, MD (301) 286-7858 (301) 286-0239 (fax) Jeffrey.Newcomer@gsfc.nasa.gov 3. Theory of Measurements The basic quantity measured by a polarimetric radar is a complex (amplitude and phase) scattering matrix for each resolution element of the radar image. This implies that AIRSAR is a multichannel system designed to maintain phase coherence between radar antennas and different channels. The polarization states used in the AIRSAR system are based on horizontal and vertical antennas. The radar is configured to measure all possible combinations available from the horizontal (H) and vertical (V) antennas (i.e. H transmitting, H receiving, and so forth). The complete scattering matrix for a resolution element can then be determined. Knowledge of the scattering matrix permits calculation of the received power for any possible combination. 4. Equipment 4.1 Sensor/Instrument Description SAR refers to a technique used to synthesize a very long antenna by combining signals (echoes) received by the radar as it moves along its flight track. NASA/JPL currently maintains and operates the AIRSAR/Topographic SAR (TOPSAR), which flies on the NASA DC-8 aircraft. The AIRSAR system is an airborne SAR that operates simultaneously in a fully polarimetric mode at three frequencies (P-, L-, and C-bands). JPL operates the radar aboard the NASA Ames Research Center DC-8 aircraft. The data collected by the AIRSAR system are processed to polarimetric imagery at JPL and provided to the BOREAS Information System (BORIS) in digital and photographic forms. The AIRSAR system provides several output products, including real-time imagery and the final processed digital products. Two of the most common digital products are the Compressed Matrix (CM) products and the Synoptic (SY) products. The real-time imagery is provided to the investigators for a SAR pass. This is a low-resolution, black-and-white, single-frequency/polarization (typically LHH) image of the entire pass. No digital data of this type are provided. Annotation of the image allows the investigators to select areas for further processing. The information on the data includes run name (name assigned to the data acquisition pass, typically the site name), Greenwich Mean Time (GMT) (day of year followed by GMT), A/C Lat-Lon, frame count, and frequency/polarization. The standard SY consists of three floating-point digital image files, one for each of the three selected channel and polarization combinations, and a color photograph. The synoptic images are 62 km along-track with a 10-15 km across- track swath. As part of the standard products, the data sets are calibrated by the ground SAR processor. During the 1993 experiment, only limited data were collected over the BOREAS study areas. In 1994, a large amount of imagery was collected and is summarized in Section 7. In 1995, a special collection effort was planned to collect imagery over an area of the SSA that had been burned the previous season. 4.1.1 Collection Environment The AIRSAR system operates within the fuselage of the DC-8 aircraft during flight. The AIRSAR was flown at medium altitudes aboard NASA’s DC-8 aircraft based at NASA JPL and provided 11-m slant range resolution at an altitude of 8,000 m. 4.1.2 Source/Platform NASA DC-8 Aircraft 4.1.3 Source/Platform Mission Objectives The objective was to acquire multipolarization and multifrequency SAR images over the BOREAS study areas and transect region. 4.1.4 Key Variables Polarization, radar frequency, radar look angle, aircraft altitude, range resolution, azimuth resolution, site lat-long coordinates, aircraft geometry. 4.1.5 Principles of Operation All DC-8 AIRSAR SY level-3b images are produced at 6 m in range and 12 m in azimuth resolutions. The NASA JPL AIRSAR is a side-looking imaging radar system that utilizes the SAR to obtain high-resolution images that represent the radar backscatter of the imaged surface at different frequencies and polarizations. 4.1.6 Sensor/Instrument Measurement Geometry During the BOREAS experiment, the instrument was located in the NASA DC-8 aircraft approximately 7,800 m above ground. The antennas are located on the port side of the aircraft looking at an angle over the site. The nominal pointing angle was 28 degrees, which covered the ground surface from approximately 28 to 72 degrees. 4.1.7 Manufacturer of Sensor/Instrument NASA’s Jet Propulsion Laboratory 4800 Oak Grove Drive Pasadena, CA 91109 (818) 354-4321 4.2 Calibration 4.2.1 Specifications In one mode of operation, this system is capable of simultaneously collecting all four polarizations (HH, HV, VH, and VV) for three frequencies: L-band (lambda ~ 24 cm), C-band (lambda ~ 6 cm), and P-band (lambda ~ 68 cm). In another mode of operation, the AIRSAR/TOPSAR system collects all four polarizations (HH, HV, VH, and VV) for two frequencies: L-band (lambda ~ 24 cm), and P-band (lambda ~ 68 cm), while operating as an interferometer at C-band to simultaneously generate topographic height data. AIRSAR/TOPSAR also has an along-track interferometer mode that is used to measure current speeds. Typical image sizes for AIRSAR/TOPSAR products are 12 km x 12 km, with 10-m resolution in both dimensions. Topographic map products generated by the TOPSAR system have been shown to have a height accuracy of 1 m in relatively flat areas and 5 m in mountainous areas. 4.2.1.1 Tolerance Each image contains detailed calibration information in the header information area. 4.2.2 Frequency of Calibration Much of the data produced by the AIRSAR are now calibrated, so that the radar backscatter measurements are in normalized radar cross-section format (m2/m2) or ?? (sigma zero). Sigma zero is the radar cross-section (measured in m2) normalized by the area of the measurement, which in this case is the pixel area in square meters. 4.2.3 Other Calibration Information Two types of complementary calibration techniques are used for AIRSAR data calibration: internal calibration, and external calibration. For the internal calibration, the information collected from the system tests that are performed regularly during the flight is used to obtain calibration parameters to be used in the AIRSAR processor. This will ensure that all the polarization channels are calibrated relative to one another at each frequency. For external calibration, which calibrates the radar cross-section of the scene absolutely and removes channel imbalance and the cross-talk, information from the scene and dihedral corner reflectors as external targets is used. Investigators who are interested in checking the accuracy of the calibration and performing other corrections themselves can request a copy of the POLCAL software and the user's manual directly from JPL. 5. Data Acquisition Methods The AIRSAR system acquires data during flights of the DC-8 aircraft. The instrument system acquires the data across the various spatial elements while the aircraft motion provides the forward motion for image acquisition. 6. Observations 6.1 Data Notes None given. 6.2 Field Notes None given. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage The BOREAS AIRSAR SY level-3b images cover sections of the Northern Study Area (NSA) and the SSA; however, a majority of the imagery was collected over the SSA. The SSA and the NSA are located in the southwest and northeast portions of the overall BOREAS region. Each image covers a 12-km along-track and 10-km across-track area. The images contain 1280 pixels in each of the approximately 5000 lines. There are just 3 dates of SY imagery over the SSA and one date over the NSA. The North American Datum of 1983 (NAD83) corner coordinates of the SSA are: Latitude Longitude -------- --------- Northwest 54.321 N 106.228 W Northeast 54.225 N 104.237 W Southwest 53.515 N 106.321 W Southeast 53.420 N 104.368 W The NAD83 corner coordinates of the NSA are: Latitude Longitude -------- --------- Northwest 56.249 N 98.825 W Northeast 56.083 N 97.234 W Southwest 55.542 N 99.045 W Southeast 55.379 N 97.489 W 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution Resolution in range: 6.66 m (across-track) Resolution in azimuth: 12.27 m. (along-track) 7.1.4 Projection The Remote Sensing Science (RSS)-16 team informed BORIS personnel that the images have been resampled into a regular spatial grid; however, the details of the projection used are not known. 7.1.5 Grid Description The RSS-16 team informed BORIS personnel that the images have been resampled into a regular spatial grid; however, the details of the gridding are not known. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage The AIRSAR SY level-3b data were collected on four dates in the period from 12- Aug-1993 to 31-Jul-1995. 7.2.2 Temporal Coverage Map Date Study Area 12-AUG-93 SSA 13-AUG-93 NSA 21-JUL-94 SSA 31-JUL-95 SSA 7.2.3 Temporal Resolution Most of the SSA Modeling Sub-Area (MSA) was covered by the AIRSAR SY images on two or three occasions from 12-Aug-1993 to 31-Jul-1995. 7.3 Data Characteristics Data characteristics of the inventory listing file are defined in the companion data definition file (airssy3b.def). 7.4 Sample Data Record Sample data format of the inventory listing file is shown in the companion data definition file (airssy3b.def). 8. Data Organization 8.1 Data Granularity The smallest unit of level-3b AIRSAR SY imagery tracked by BORIS is a single three-band scene. All of the RSS-16 Level-3b DC-8 AIRSAR SY Images are contained in one dataset. 8.2 Data Format(s) The inventory listing file contains numerical and character fields of varying length separated by commas. The character fields are enclosed with a single apostrophe marks. There are no spaces between the fields. Sample data records are shown in the companion data definition file (airssy3b.def). A level-3b AIRSAR SY image from BORIS is contained in three files. Each record of a level-3b AIRSAR SY data file contains 5120 bytes. The first three records in each file contain header information. The number of data records in a file varies depending on the length of the flight line. Each data record of 5,120 bytes contains 1,280 pixels, each stored in a 32-bit (4-byte) binary VAX floating point value. More specific information is as follows: FILE 1 (5,120-byte records) - JPL AIRSAR New Header Record (Record 1) * 20 records, each containing 50 American Standard Code for Information Interchange (ASCII) characters. * 4,120 fill bytes. - JPL AIRSAR Old Header Record (Record 2) * 64 records, each containing 50 ASCII characters. * 1,920 fill bytes. - JPL AIRSAR Parameter Header Record (Record 3) * 87 records, each containing 50 ASCII characters. * 770 fill bytes. - JPL AIRSAR SY image data records (Record 4 to end of file) (1,280 pixels stored as 32-bit VAX floating point values) FILE 2 (5,120-byte records) - JPL AIRSAR New Header Record (Record 1) * 20 records, each containing 50 ASCII characters. * 4,120 fill bytes. - JPL AIRSAR Old Header Record (Record 2) * 64 records, each containing 50 ASCII characters. * 1,920 fill bytes. - JPL AIRSAR Parameter Header Record (Record 3) * 87 records, each containing 50 ASCII characters. * 770 fill bytes. - JPL AIRSAR SY image data records (Record 4 to end of file) (1,280 pixels stored as 32-bit VAX floating point values) FILE 3 (5,120-byte records) - JPL AIRSAR New Header Record (Record 1) * 20 records, each containing 50 ASCII characters. * 4,120 fill bytes. - JPL AIRSAR Old Header Record (Record 2) * 64 records, each containing 50 ASCII characters. * 1,920 fill bytes. - JPL AIRSAR Parameter Header Record (Record 3) * 87 records, each containing 50 ASCII characters. * 770 fill bytes. - JPL AIRSAR SY image data records (Record 4 to end of file) (1,280 pixels stored as 32-bit VAX floating point values) Sample data records are shown in the companion data definition file (airssy3b.def). 9. Data Manipulations 9.1 Formulae None. 9.1.1 Derivation Techniques and Algorithms None given. 9.2 Data Processing Sequence 9.2.1 Processing Steps BORIS staff makes the AIRSAR SY level-3b images available by: 1) Duplicating the JPL-delivered images for backup purposes. 2) Extracting pertinent header information from the images for use in inventorying the level-3b image by date and time in the online data base. 3) Reviewing the content of the extracted header information for potential problems/anomalies, 4) Loading the needed information into the on-line data base. 9.2.2 Processing Changes None. 9.3 Calculations 9.3.1 Special Corrections/Adjustments None given. 9.3.2 Calculated Variables None given. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error None given. 10.2 Quality Assessment 10.2.1 Data Validation by Source None given. 10.2.2 Confidence Level/Accuracy Judgment None given. 10.2.3 Measurement Error for Parameters None given. 10.2.4 Additional Quality Assessments None given. 10.2.5 Data Verification by Data Center BORIS staff reviews the images using developed software that was designed based on data product format documents received from JPL personnel. The software reads through the data products on tape and summarizes the contents in ASCII files on disk. These files are reviewed visually by BORIS personnel for anomalous items. 11. Notes 11.1 Limitations of the Data None given. 11.2 Known Problems with the Data None given. 11.3 Usage Guidance None given. 11.4 Other Relevant Information None given. 12. Application of the Data Set AIRSAR images are used to estimate surface parameters such as canopy water content, soil moisture, and stand biomass and density. 13. Future Modifications and Plans None given. 14. Software 14.1 Software Description BORIS staff developed software and command procedures to: 1) Check and extract information from level-3b AIRSAR SY images on tape and write the information to ASCII files on disk. 2) Read the ASCII disk file and log the level-3b AIRSAR SY images into the Oracle data base tables. The software mentioned under items 1 and 2 is written in the C language and is operational on VAX 6410 and MicroVAX 3100 systems at Goddard Space flight Center (GSFC). The primary dependencies in the software are the tape Input/Output (I/O) library and the Oracle data base utility routines. 14.2 Software Access All of the described software is available upon request. BORIS staff would appreciate knowing of any problems discovered with the software, but cannot promise to fix them. 15. Data Access 15.1 Contact for Data Center/Data Access Information These BOREAS data are available from the Earth Observing System Data and Information System (EOS-DIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The BOREAS contact at ORNL is: ORNL DAAC User Services Oak Ridge National Laboratory Oak Ridge, TN (865) 241-3952 ornldaac@ornl.gov ornl@eos.nasa.gov 15.2 Procedures for Obtaining Data BOREAS data may be obtained through the ORNL DAAC World Wide Web site at http://www-eosdis.ornl.gov/ or users may place requests for data by telephone, electronic mail, or fax. 15.3 Output Products and Availability Requested data can be provided electronically on the ORNL DAAC's anonymous FTP site or on various media including, CD-ROMs, 8-MM tapes, or diskettes. The complete set of BOREAS data CD-ROMs, entitled "Collected Data of the Boreal Ecosystem-Atmosphere Study", edited by Newcomer, J., et al., NASA, 1999, are also available. 16. Output Products and Availability 16.1 Tape Products The AIRSAR level-3b SY data can be made available on 8-mm or Digital Archive Tape (DAT) media. 16.2 Film Products None. 16.3 Other Products During the data acquisition flight, 35-mm photographs were taken of the areas imaged by the AIRSAR system. Anyone interested in these photographs should contact Dr. Sasan Saatchi (see Section 2.3. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation NASA JPL. Date unknown. “AIRSAR Data Formats,” Chapter 4. NASA JPL. 1995. AIRSAR Integrated Processor Documentation: DATA FORMATS. Version 0.01. 17.2 Journal Articles and Study Reports Sellers, P.and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94). Sellers, P.and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). Sellers, P.and F. Hall. 1997. BOREAS Overview Paper. JGR Special Issue. Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPSDOC 94). Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPSDOC 96). Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J. Ranson, D. Lettenmaier, and D.E. Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and early results from the 1994 field year. Bulletin of the American Meteorological Society. 76(9):1549-1577. van Zyl, J., The AIRSAR System, JPL document, 1992. van Zyl, J.,1995, AIRSAR Integrated Processor Documentation, version 0.01, April 21, 1995 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List of Acronyms AIRSAR - Airborne Synthetic Aperture Radar ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System BPI - Bytes Per Inch CCT - Computer Compatible Tape CM - Compressed Matrix DAAC - Distributed Active Archive Center DAT - Digital Archive Tape EOS - Earth Observing System EOSDIS - EOS Data and Information System GMT - Greenwich Mean Time GSFC - Goddard Space Flight Center JPL - Jet Propulsion Laboratory MSA - Modeling Sub-Area NAD83 - North American Datum of 1983 NASA - National Aeronautics and Space Administration NSA - Northern Study Area ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park RSS - Remote Sensing Science SAR - Synthetic Aperture Radar SSA - Southern Study Area SY - Synoptic TORSAR - Topographic SAR URL - Uniform Resource Locator 20. Document Information 20.1 Document Revision Date Written: 31-Jul-1995 Last Updated: 05-Jun-1998 20.2 Document Review Date(s) BORIS Review: 05-Jun-1998 Science Review: 20.3 Document ID 20.4 Citation The AIRSAR data were provided by the Radar Data Center at NASA’s Jet Propulsion Laboratory. 20.5 Document Curator 20.6 Document URL Keywords: SAR Radar JPL AIRSAR RSS16_AIRSAR_SY.doc 06/11/98