AIRMISR_KONVEX Data Set Readme 1.0 Introduction This file contains information about the AirMISR data taken during the KONza Validation EXperiment(KONVEX) including implementation of the sample READ software. The KONVEX experiment spanned the time 11 - 18 July, 1999. The data included in this data set is for 13 July 1999, flight #36 only. The data are provided by the Jet Propulsion Laboratory (JPL) in Pasadena, California. This data set is available through the Langley Atmospheric Science Data Center as: AIRMISR_KONVEX Each data file contains the Level 1B1 Radiometric product or the Level 1B2 Georectified radiance product from one of the 9 camera angles from one run of each flight. Additional information about the AirMISR data can be obtained at the following location: http://www-misr.jpl.nasa.gov/mission/air.html Additional information about tools to read and view AirMISR data can be obtained at the following location: http://eosweb.larc.nasa.gov/PRODOCS/misr/misr_tools.html This Readme file includes the following sections: Section 2.0 - Data Set Description Section 3.0 - Data Format and Packaging Section 4.0 - Science Parameter Information Section 5.0 - Description of Sample Read Software Section 6.0 - Implementing Sample Read Software Section 7.0 - Sample Output Section 8.0 - Additional Information If there are questions about using the AIRMISR_KONVEX sample read software, please contact the Langley Science User and Data Services (SUDS) office at: Langley Atmospheric Science Data Center NASA Langley Research Center Mail Stop 157D, 2 S. Wright St. Hampton, VA 23681-2199 USA E-Mail: larc@eos.nasa.gov Phone: (757)864-8656 FAX: (757)864-8807 2.0 Data Set Information The Airborne Multi-angle Imaging SpectroRadiometer (AirMISR) is an airborne instrument for obtaining multi-angle imagery similar to that of the satellite-borne Multi-angle Imaging SpectroRadiometer (MISR) instrument, which is designed to contribute to studies of the Earth's ecology and climate. AirMISR flies on the NASA ER-2 aircraft. The instrument was built for NASA by the Jet Propulsion Laboratory in Pasadena, California. Unlike the spaceborne MISR instrument, which has nine cameras oriented at various angles, AirMISR utilizes a single camera in a pivoting gimbal mount. In general, a data run by the ER-2 aircraft is divided into nine segments, each with the camera positioned to a particular MISR look angle. The gimbal rotates between successive flight segments, such that each segment acquires data over the same area on the ground as the previous segment. This process is repeated until all nine angles of the target area are collected. The swath width, which varies from 11 km in the nadir to 32 km at the most oblique angle, is governed by the camera's instantaneous field-of-view of 7 meters cross-track x 6 meters along-track in the nadir view and 21 meters x 55 meters at the most oblique angle. The along-track image length at each angle is dictated by the timing required to obtain overlap imagery at all angles, and varies from about 9 km in the nadir to 26 km at the most oblique angle. Thus, the nadir image dictates the area of overlap that is obtained from all nine angles. The use of a single camera to provide coverage at all nine angles is possible because AirMISR is not attempting to obtain continuous, global coverage, as is the case from the spaceborne MISR. This approach ensures identical calibration at all angles, a useful feature in utilizing the instrument as part of the MISR calibration. The 9 camera viewing angles are: 0 degrees or nadir 26.1 degrees, fore and aft 45.6 degrees, fore and aft 60.0 degrees, fore and aft 70.5 degrees, fore and aft For each of the camera angles, images are obtained at 4 spectral bands. The spectral bands can be used to identify vegetation and aerosols, estimate surface reflectance and ocean color studies. The center wavelength of the 4 spectral bands are: 443 nanometers, blue 555 nanometers, green 670 nanometers, red 865 nanometers, near-infrared Two types of AirMISR data products are available through the Langley Atmospheric Science Data Center. They are the Level 1 Radiometric product and the Level 1 Georectified radiance product (L1B2). The Level 1 Radiometric product contains data that have been scaled to convert the digital output of the cameras to radiances and have been conditioned to remove instrument-dependent effects. Additionally, all radiances are adjusted to remove slight spectral sensitivity differences among the detector elements of each spectral band. These data have a 7 meter spatial resolution. The Level 1 Georectified radiance product contains the Level 1 radiometric product that have been resampled to a 27.5 meter spatial resolution and have been mapped into a standard Universal Transverse Mercator (UTM) map projection. Initially the data are registered to each camera angle and to the ground. This processing is necessary because the nine views of each point on the ground are not acquired simultaneously. Once the map grid center points are located in the AirMISR imagery through the process of georectification, a radiance value obtained from the surrounding AirMISR pixels needs to be assigned to that map grid center. Bilinear interpolation is used as the basis for computing the new radiance. A UTM grid point falling somewhere in the image data will have up to 4 surrounding points. The bilinear interpolated value is obtained using the fractional distance of the interpolation point in cross-track direction and the fractional distance in the along the track direction. 2.1 Data Quality 2.1.1 Radiometric Data Quality It is believed that the July 13, 1999 AirMISR flight in support of the KONVEX campaign was a success. The camera successfully slewed to all nine angle positions. The radiometric accuracy and signal-to-noise ratio during this specific mission is as good as the Science Team has reported in the literature. Individual product files contain metadata identifying dropped/corrupt lines, saturated pixels and related image quality parameters. The radiometric calibration of AirMISR has been done using the same procedures as used to calibrate the MISR cameras; the reported radiometric calibration uncertainties are therefore the same as reported for MISR. (The exception is the camera-to-camera uncertainty, which is believed to be smaller for AirMISR, as the aircraft instrument consists of one gimballed camera). Thus, it is believed that the radiometric uncertainties are small, and the camera signal-to-noise ratio is high. The values quoted for the systematic component of the radiometric uncertainty, in fractional units, are: abs_sys_error 0.016 cam_sys_error 0.000 band_sys_error 0.007 pixel_sys_error 0.003 That is, the systematic component of the absolute, camera-to-camera, band-to-band, and pixel-to-pixel are given above. These systematic components are combined with signal-to-noise (SNR), to determine the total error uncertainties. As SNR is signal dependent, the uncertainties are likewise signal dependent. SNR, at two radiance input levels, are as follows: SNR(equivalent-reflectance=1.0) ~ 1000 SNR(equivalent-reflectance=0.05) ~ 200 Using these, the total radiometric uncertainties can be determined: abs_total_error=sqrt(abs_sys_error^2+(1/SNR)^2) cam_total_error=sqrt(2)/SNR band_total_error=sqrt(2)*sqrt(band_sys_error^2+(1/SNR)^2) pixel_total_error=sqrt(2)*sqrt(pixel_sys_error^2+(1/SNR)^2) References on the radiometric calibration of AirMISR and MISR are listed in Section 8.0. Additional references are available from the MISR web site at http://www-misr.jpl.nasa.gov 2.1.2 Geometric Data Quality The geometric calibration has been performed prior to orthorectification to the UTM map projection grid. A set of ground control points collected from USGS 1:24000 topographic maps were used to remove static errors in the camera pointing and airplane position. Using calibration results, geolocation errors of about 1000 meters for nadir view to up to 6000 meters for most oblique views are reduced down to 30 meters for nadir and to up to 300 meters for the most oblique view angles. The remaining errors can be regarded as a result of the dynamic errors in airplane attitude and position which are not modeled in the current calibration algorithm. 2.2 Science Point of Contact Carol J. Bruegge, Ph.D. MISR Instrument Scientist JPL MS 169-237 4800 Oak Grove Dr. Pasadena, CA 91109-8099 Phone: 818-354-4956 Fax: 818-393-4619 E-mail: Carol.J.Bruegge@Jpl.Nasa.Gov 3.0 Data Format and Packaging 3.1 Data Format The L1B1 data are in HDF format. The L1B2 data are in HDF-EOS format, but can be read as HDF format. Further information about HDF-EOS (Hierarchical Data Format - Earth Observing System) can be found at the HDF-EOS web site, http://hdfeos.org/ Information regarding HDF format is available at the following web sites: http://hdf.ncsa.uiuc.edu/ http://eosweb.larc.nasa.gov/HBDOCS/hdf.html 3.2 Data File Naming Convention The AIRMISR_KONVEX data files are named in the following manner, where all elements within the <> symbols are variable. AIRMISR_RP___F_.hdf AIRMISR_GP___F_.hdf AIRMISR_RP: native HDF file containing AirMISR Level 1B1 radiometrically calibrated product which is processed to sensor units, but not geolocated. AIRMISR_GP: HDF-EOS file containing AirMISR Level 1B2 geometrically calibrated product which is L1B1 data that has been geolocated. : date and time in UTC computed from ER-2 navigation for image mid-point in the downtrack direction. : AirMISR camera angles, SF - stowed or "homed" position DF - fore, 70.5 degrees viewing angle CF - fore, 60. degrees viewing angle BF - fore, 45.6 degrees viewing angle AF - fore, 26.1 degrees viewing angle AN - nadir, 0 degrees viewing angle AA - aft, 26.1 degrees viewing angle BA - aft, 45.6 degrees viewing angle CA - aft, 60. degrees viewing angle DA - aft, 70.5 degrees viewing angle SA - stowed or "homed" position : defines which product format was used in creating the product. The format version refers to the entire system used to generate products, so L1B1 and L1B2 format versions will change together. Files processed after 5/31/2001 have a format version of F02. The format version for earlier files is F01. Note that this refers to the processing date, not the flight date. : defines the content of a file. The value is incremented every time the data is reprocessed. The value is reset to 01 when a new format version is created. Example file names: AIRMISR_RP_990713_172523_CA_F01_01.hdf AirMISR Level 1B1 Radiometric product taken on July 13, 1999 with the image mid-point at 17:25:23 UTC. The viewing angle is 60. deg. aft, L1B1 format version 01 and file version 01. AIRMISR_GP_990713_161018_DF_F01_02.hdf AirMISR Level 1B2 Georectified radiance product taken on July 13, 1999 with the image mid-point at 16:10:18 UTC. Data is for viewing angle 70.5 deg. fore, L1B2 format version is 01 and the file version is 02. 3.3 Image Naming Convention The AIRMISR_KONVEX "RP" (L1B1) data files have associated gif images. The images are named using the same naming convention as the data files with the addition of the image size and spectral band. For this data set only the red band images are available. AIRMISR_RP___F_...gif : blue, green, red and near-infrared spectral bands. : thumb - 100 x 100 pixels browse - 640 x 480 pixels full - 1280 x 963 pixels Example image names: AIRMISR_RP_990713_172047_BF_F01_01.red.thumb.gif AirMISR Level 1B1 browse image taken on July 13, 1999 with the image mid-point at 11:08:56 UTC. The viewing angle is 45.6 deg. fore, format version 01, file version 01, red spectral band centered at 670 nanometers, thumbnail size. 4.0 Science Parameter Information for L1B2 data files 4.1 Grid Field Parameters For detailed information regarding file contents, please obtain the AirMISR Data Products Specifications (DPS) document at the following URL: http://eosweb.larc.nasa.gov/PRODOCS/airmisr/table_airmisr.html ----------------------------------------------------------------- Field Description Units ----------------------------------------------------------------- Terrain Blue scaled radiance unitless Terrain Blue DQI data quality index unitless Terrain Green scaled radiance unitless Terrain Green DQI data quality index unitless Terrain Red scaled radiance unitless Terrain Red DQI data quality index unitless Terrain Infrared scaled radiance unitless Terrain Infrared DQI data quality index unitless Ellipsoid Blue scaled radiance unitless Ellipsoid Blue DQI data quality index unitless Ellipsoid Green scaled radiance unitless Ellipsoid Green DQI data quality index unitless Ellipsoid Red scaled radiance unitless Ellipsoid Red DQI data quality index unitless Ellipsoid Infrared scaled radiance unitless Ellipsoid Infrared DQI data quality index unitless Sun Azimuth solar azimuth angle degrees Sun Zenith solar zenith angle degrees View Azimuth viewing azimuth angle degrees View Zenith viewing zenith angle degrees ----------------------------------------------------------------- The Terrain and Ellipsoid fields listed above refer to the 2 projections used in georectifying the data. The scaled radiance is the total-band, standardized spectral response weighted. To compute actual radiance multiply these values by their corresponding scale factor listed in the metadata below. The sample read software described in Sections 5 - 7, performs these computations. A DQI value of 0 indicates a good data value in the corresponding radiance file and a value of 255 indicates the radiance data value is set to the fill value. 4.2 Grid Attribute (Metadata) Parameters ----------------------------------------------------------------- Field (units) Description ----------------------------------------------------------------- UL Corner (degrees) upper left corner of data region (latitude, longitude) LR Corner (degrees) lower right corner of data region (latitude, longitude) YDim:AirMisr (N/A) Y coordinates XDim:AirMisr (N/A) X coordinates StructMetadata.0 (N/A) grid structure information Rad_scale_factor radiance scale factor (4) (Wm-2um-1sr-1) 1=blue;2=green;3=red;4=nir std_inband_solar_wgted_height solar and in-band irradiances standardized response weighted (4) (Wm-2um-1) 1=blue;2=green;3=red;4=nir std_inband_solar_wgted_center_wave center wavelength, solar and (nm) in-band standardized response weighted (4) 1=blue;2=green;3=red;4=nir std_inband_solar_wgted_width bandwidth, solar and in-band (nm) standardized response weighted (4) 1=blue;2=green;3=red;4=ir std_solar_wgted_height solar irradiances, standardized (Wm-2um-1) response weighted (4) 1=blue;2=green;3=red;4=nir std_solar_wgted_center_wave center wavelength, solar and (nm) standardized response weighted (4) 1=blue;2=green;3=red;4=nir std_solar_wgted_width bandwidth, solar and standardized (nm) response weighted (4) 1=blue;2=green;3=red;4=nir band_wgted_max_rad band weighted maximum radiance (4) (Wm-2um-1sr-1]) 1=blue;2=green;3=red;4=inr Minimum_image_time (UTC) beginning image time Maximum_image_time (UTC) ending image time Sun_distance Earth Sun distance (Astronomical units) 5.0 Description of Sample Read Software Currently, there is one sample read program which reads the Level 1B2 Georectified radiance product ("GP" files) only, read_airmisr.pro. This software does not read the Level 1B1 Radiance product ("RP" files). The software is written in the IDL programming language. It has been tested on the following computers and operating systems: Computer Operating System IDL Version ---------------- ---------------- ----------- Sun Sparc Solaris 2.6 5.4 SGI Origin 2000 IRIX 6.5 5.3 IBM PC Windows 2000 5.5 This program is written as an example of how to read AIRMISR_KONVEX Georectified radiance product and to compute actual radiances from the scaled values and the scale factor. As delivered, it prompts the user to select an input filename and parameters to output. It reads in the selected fields from the file, computes radiance if selected and writes the selections to the output file in ASCII format. The output file is given the same name as the selected AirMISR file, but the ".hdf" file suffix is replaced with "_output". It is written to the current default directory. A dialog box displays the filenames for input file selection. The dialog box is created with a call to the dialog_pickfile procedure which assumes that the data files are in the current directory. The "Filter" parameter in the call to dialog_pickfile may be modified to specify an alternate directory. 6.0 Implementing the Sample Read Software The file read_airmisr.pro contains several procedures, so the entire file must be compiled before it can be run. To do this, the user must first start up IDL by typing "idl". At the IDL prompt, type ".compile read_airmisr", then type the program name, "read_airmisr" to start the program. Alternatively, the IDL development environment can be used. To start IDL this way, type "idlde" at the unix prompt or select IDL from the Start menu on a PC. Under File, choose "Open" and then select the file read_airmisr.pro. Under Run, choose "Compile read_airmisr.pro". Finally, under Run, choose "Run read_airmisr". 7.0 Sample Output The read_airmisr.pro program can be used to read any of the AIRMISR_KONVEX Georectified radiance product files, i.e., "GP" files. The following is a sample session showing compilation, execution of the program and portions of the output file. Compilation and Execution ------------------------- IDL> .compile read_airmisr % Compiled module: READ_AIRMISR. % Compiled module: GET_METADATA. % Compiled module: GET_GRID_FIELDS. % Compiled module: MAKE_LIST. % Compiled module: WRITE_OUTPUT. % Compiled module: GET_FILE_INFO. % Compiled module: SELECTTOOL. % Compiled module: SELECTTOOL_EVENT. IDL> read_airmisr ***************************************************************** * * * * * read_airmisr.pro * * * * Version: 2.0 * * * * Date: July 8, 2002 * * * * Contact: Langley Atmospheric Science Data Center * * NASA Langley Research Center * * Mail Stop 157D * * 2 South Wright Street * * Hampton, Virginia 23681-2199 * * U.S.A. * * * * E-mail: larc@eos.nasa.gov * * Phone: (757)864-8656 * * FAX: (757)864-8807 * * * ***************************************************************** Input Filename AIRMISR_GP_010721_162241_AN_F02_01.hdf % Loaded DLM: HDF. CHOOSE THE PARAMETERS TO BE WRITTEN TO THE OUTPUT FILE % Compiled module: STRSPLIT. % Compiled module: CW_PDMENU. % Compiled module: XMANAGER. End of selection The following 3 parameters were chosen: Terrain Red UL Corner (deg): Latitude Longitude Sun_distance **************** Begin reading data ********************* WRITING TO OUTPUT ---> UL Corner (deg): Latitude Longitude WRITING TO OUTPUT ---> Sun_distance WRITING TO OUTPUT ---> Terrain Red **************** THE PROGRAM HAS RUN TO COMPLETION!! ********************* Output File (in part) --------------------- File: AIRMISR_GP_010721_162241_AN_F02_01.hdf Image Start Time = 2001-07-21T16:22:17.788100Z Image End Time = 2001-07-21T16:23:04.993700Z GridName="AirMisr" XDim=2078 YDim=2256 UpperLeftPointMtrs=(311551.000000,4349910.000000) LowerRightMtrs=(368696.000000,4287870.000000) Projection=GCTP_UTM ZoneCode=18 SphereCode=12 VALUES for Metadata ================================================================================ Name = UL Corner (deg): Latitude Longitude Data = 39.278068 -77.184764 -------------------------------------------------------------------------------- Name = Sun_distance Data = 1.0160355 -------------------------------------------------------------------------------- VALUES for Grid Fields ================================================================================ Name = Terrain Red Scale Value = 0.038470935 Fill Value = 65535 Data = 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 ... skipping lines 65535.000 65535.000 56.282978 44.895581 27.891428 28.391550 34.816196 28.276137 30.815219 61.899735 50.319983 35.547144 ... skipping to the end of the file 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 65535.000 ------------------------------------------------------------------------------ 8.0 Additional Information 8.1 References Bruegge, Carol J., Wedad A. Abdou, Nadine L. Chrien, Barbara J. Gaitley (1998). AirMISR spectral and radiometric performance studies. In Earth Observing System III, Proc. SPIE 3439, San Diego, CA, 19-21 July. Bruegge, C.J., N. L. Chrien, R. A. Kahn, J. V. Martonchik, David Diner (1998). MISR radiometric uncertainty analyses and their utilization within geophysical retrievals. Conference issue: New Developments and Applications in Optical Radiometry (NEWRAD '97), Metrologia., 35, 571-579. Bruegge, C.J., V.G. Duval, N.L. Chrien, R.P. Korechoff, B.J. Gaitley, and E.B. Hochberg (1998). MISR prelaunch instrument calibration and characterization results. IEEE Trans. Geosci. Rem. Sens., Vol. 36, pp. 1186-1198. Chrien, Nadine L., Carol J. Bruegge, Barbara J. Gaitley (2000). AirMISR laboratory calibration and in-flight performance results. Submitted to Remote Sens. Environment., December 1998. Last Updated July 10, 2002