BOREAS Level-2 NS001 TMS Images: Reflectance and Temperatures in BSQ Format Summary For BOREAS, the NS001 TMS images, along with the other remotely sensed data, were collected to provide spatially extensive information over the primary study areas. This information includes detailed land cover and biophysical parameter maps such as fPAR and LAI. Collection of the NS001 images occurred over the study areas during the 1994 field campaigns. The Level-2 NS001 data are atmospherically corrected versions of some of the best original NS001 imagery and cover the dates of 19-Apr-1994, 07-Jun-1994, 21-Jul-1994, 08-Aug-1994, and 16-Sep-1994. The data are not geographically/geometrically corrected; however, files of relative X and Y coordinates for each image pixel were derived by using the C130 INS data in an NS001 scan model. The data are provided in binary image format files. Note that some of the data files on the BOREAS CD-ROMs have been compressed using the Gzip program. See Section 8.2 for details. Note also that the top portion of the ASCII header file in each Level-2 NS001 image product indicates that the band 8 data are 'Scaled Reflectance' when in fact they are 'Scaled Temperatures.' 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 Level-2 NS001 TMS Images: Reflectance and Temperatures in BSQ Format 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, processing, and archiving of eight-band NS001 Thematic Mapper Simulator (TMS) Multispectral Scanner (MSS) data collected on National Aeronautics and Space Administration's (NASA) C-130 aircraft. The NS001 provided spectral image data very similar to that of the Landsat Thematic Mapper (TM). 1.3 Objective/Purpose For BOREAS, the NS001 TMS imagery, along with the other remotely sensed images, was collected to provide spatially extensive information over the primary study areas. This information includes detailed land cover and biophysical parameter maps such as fraction of Photosynthetically Active Radiation (fPAR), and Leaf Area Index (LAI). The Level-2 products contain atmospherically corrected reflectance and temperature bands in addition to ‘good’ relative X and Y coordinates of each pixel. 1.4 Summary of Parameters NS001 Level-2 data in the BOREAS Information System (BORIS) consist of 21 files per flight line and as a set contain the following parameters: Descriptive information as American Standard Code for Information Interchange (ASCII) text records, reflectance values for image bands 1 to 7, temperature values for image band 8, housekeeping information for each band, per pixel relative X and Y pixel coordinates, and per pixel view zenith and azimuth angles. 1.5 Discussion BOREAS Information System (BORIS) personnel processed the NS001 TMS Level-0 images by: 1) Extracting pertinent header information from the Level-0 image product and placing it in an ASCII file on disk. 2) Reading the information in the disk file and loading the online data base with needed information. 3) Developing software to calculate the relative X and Y pixel positions from the C130 Inertial Navigation System (INS) data and providing it to NASA Ames Research Center (ARC) personnel. NASA ARC personnel created the Level-2 NS001 TMS imagery by: 1) Obtaining the pertinent Level-0 NS001 imagery from BORIS. 2) Obtaining optical depth data from BORIS. 3) Obtaining radiosonde data from BORIS. 4) Modeling the path transmittance and path radiative emission (thermal channel) using a Moderate Resolution Model of LOWTRAN7 (MODTRAN). 5) Modeling the path water vapor column concentration and downwelling irradiance using the Second Simulation of the Satellite Signal in the Solar Spectrum (6S). 6) Processing the imagery using NASA ARC's Image Atmospheric Correction (Imagecor) program. 7) Using the BORIS software and C130 INS data to calculate files of X and Y coordinates. 8) Returning the processed files to BORIS. 1.6 Related Data Sets BOREAS Level-0 C-130 Navigation Data BOREAS Level-0 C-130 Aerial Photography BOREAS RSS-02 Level-1b ASAS Imagery: At-sensor Radiance in BSQ Format BOREAS Level-1B MAS Imagery: At-sensor Radiance, Relative X and Y Coordinates BOREAS Level-2 MAS Imagery: Reflectance and Temperatures in BSQ Format BOREAS Level-0 TIMS Imagery: Digital Counts in BIL Format 2. Investigator(s) 2.1 Investigator(s) Name and Title Brad Lobitz Johnson Controls NASAARC Richard Strub Raytheon STX Corp. NASA GSFC 2.2 Title of Investigation BOREAS Staff Science Aircraft Data Acquisition Program 2.3 Contact Information Contact 1 ------------------- Brad Lobitz Johnson Controls, Inc NASA ARC Moffett Field, CA (650) 604-3223 blobitz@mail.arc.nasa.gov Contact 2 ------------------- Richard Strub Raytheon STX Corporation NASA GSFC Greenbelt, MD (301) 286-4545 Richard.Strub@gsfc.nasa.gov 3. Theory of Measurements The NASA Earth Resources Aircraft Program at ARC operates the C-130 aircraft to acquire data for Earth science research. The NS001 MSS used on the C-130 aircraft collects radiance measurements in the seven Landsat-4 and -5 TM bands plus a band from 1,000 to 1,300 nm. Therefore, when reflected or emitted radiation from Earth surface features is measured from the aircraft, inferences can be made about Landsat satellite measurements. Thematic considerations dictated, within technical constraints, the choice of spectral band position and width in the NS001 sensor. Eight bands were selected seven of which correspond to Landsat TM bands. These bands were chosen after many years of analysis for their value in discrimination of several Earth surface features. A blue (0.45 to 0.52 µm) band provides increased penetration of water bodies and supports analyses of land use, soil, and vegetation characteristics. The lower wavelength cutoff is just below the peak transmittance of clear water, while the upper wavelength cutoff is the limit of blue chlorophyll absorption for healthy green vegetation. Wavelengths below 450 nm are substantially influenced by atmospheric scattering and absorption. A green (0.52 to 0.60 µm) band spans the region between the blue and red chloro- phyll absorption bands and therefore corresponds to the green reflectance of healthy vegetation. A red (0.63 to 0.69 µm) band includes the chlorophyll absorption band of healthy green vegetation and represents one of the most important bands for vegetation discrimination. It is also useful for soil boundary and geological boundary delineations. A reflective-infrared (0.76 to 0.90 µm) band is especially responsive to the amount of vegetation biomass present in a scene. It is useful for crop identification and emphasizes soil- crop and land-water contrasts. Two of the three mid-infrared (1.00 to 1.30; 1.55 to 1.75 µm) bands are sensi- tive to the turgidity or amount of water in plants. Such information is useful in crop drought studies and plant vigor investigations. In addition, these are two of the few bands that can be used to discriminate between clouds, snow, and ice, which is very important in hydrologic research. The other mid-infrared band (2.08 to 2.35 µm) is important for the discrimination of geologic rock formations. It has been shown to be particularly effective in identifying zones of hydrothermal alteration in rocks. They final band is the thermal infrared (10.4 to 12.5 µm) band, which measures the amount of infrared radiant flux emitted from surfaces. The apparent temperature is a function of the emissivities and true or kinetic temperature of the surface. It is useful for locating geothermal activity, thermal inertia mapping for geologic investigations, vegetation classification, vegetation stress analysis, and soil moisture studies. 4. Equipment 4.1 Sensor/Instrument Description The NS001 TMS instrument is designed to simulate spectral, spatial, and radiometric characteristics of the TM sensor on the Landsat-4 and -5 spacecraft. The NS001 is generally flown at medium altitudes aboard NASA's C-130 aircraft based at NASA ARC and provides 12.2 meter resolution at nadir at an altitude of 4,878 meters (16,000 feet). The NS001 sensor differs slightly from the Landsat TM instruments. It has seven spectral channels that are very similar to those of the TM sensor, but, it has an additional infrared channel, as follows: Comparable NS001 Channel Wavelength, µm Landsat TM Band ------------- -------------- --------------- 1 0.45-0.52 1 2 0.52-0.60 2 3 0.63-0.69 3 4 0.76-0.90 4 5 1.00-1.30 - 6 1.55-1.75 5 7 2.08-2.35 7 8 10.40-12.5 6 4.1.1 Collection Environment The C-130 aircraft flies at altitudes ranging from 5,000 to 7,000 meters. 4.1.2 Source/Platform NASA's C-130 Earth Resources Aircraft. 4.1.3 Source/Platform Mission Objectives The original purpose of the scanner was to provide low-altitude data in the Landsat TM bands for analysis prior to the launch of the satellite and to provide calibration information from under-flights subsequent to the launch of the satellite. 4.1.4 Key Variables Emitted radiation, reflected radiation, and temperature. 4.1.5 Principles of Operation Design parameters of the NS001 are based on the specifications of the Landsat TM with respect to spectral band characteristics. A single spectrometer disperses the energy to cover the first six bands from 0.45 µm to 1.75 µm. An array of silicon, germanium, and indium antimonide detectors is used. Band 7 is separated by a dichroic bandpass filter. The eighth band, in the 10.4-µm to 12.5-µm region, is detected by a cooled mercury-cadmium-telluride detector. Variable velocity over height (V/H) conditions are compensated by a variable speed motor that drives the scan mirror. Each channel uses a preamplifier to provide initial video amplification. Gain and level control of video signals are adjustable from the operator's control panel. Each channel is digitized to an 8-bit resolution and is multiplexed with calibration and housekeeping data. 4.1.6 Sensor/Instrument Measurement Geometry Instananeous Field of View (IFOV) 2.5 mrad Total Scan Angle 100 degrees Pixels/Scan Line 699 Sensor footprint is 12.2 by 12.2 m at nadir at 4,878 meters altitude. 4.1.7 Manufacturer of Sensor/Instrument NASA/Lyndon B. Johnson Space Center Houston, TX Lockheed Electronics Company, Inc. Systems and Services Division Houston, TX 4.2 Calibration The NS001 includes two full-aperture blackbodies and one integrating sphere within the scan mirror cavity. They are viewed each scan by the instrument and the responses are embedded in the data stream. Blackbody temperatures and lamp current data are multiplexed with scanner output data. The blackbody irradiance is determined by its monitored temperature and estimated emissivity. The blackbodies are also cross-checked periodically by comparing the NS001 responses to the blackbodies and an external precision blackbody. The internal sphere is calibrated by reference to an external light source. The principal source used for calibrating the internal sphere for BOREAS in 1994 was a 76-cm-diameter integrating sphere owned by ARC and calibrated by the Standards and Calibration Office at GSFC. The sphere contains 12 internally mounted quartz halogen lamps. Estimated uncertainty in the calibration of the sphere is +/-5%. The April 1994 calibration of the sphere was used to calibrate the internal calibration source in the NS001 in 1994. 4.2.1 Specifications The wavelength range (in µm) of the bands for the NS001 are: Band Detector Wavelength NE(delta P) % ------ -------- ------------- ------------- 1 Si 0.458 - 0.519 0.5 2 Si 0.529 - 0.603 0.5 3 Si 0.633 - 0.697 0.5 4 Si 0.767 - 0.910 0.5 5 Ge 1.13 - 1.35 1.0 6 Ge 1.57 - 1.71 1.0 7 InSb 2.10 - 2.38 2.0 8 HgCdTe 10.9 - 12.3 NE(delta T) = 0.25 K DESIGN DATA: IFOV 2.5 milliradians Across-track field of view 100 degrees Nominal aperture diameter 10.16 cm Effective aperture area 72.4 cm^2 f/number 1.85 Primary focal length 18.8 cm In flight calibration Integrating sphere and two controllable blackbodies Short-wavelength array temperature 255 K V/H range Variable 0.025 to 0.25 Scan rate Variable 10 to 100 scans/sec. Scan speed stability One-third of the IFOV, scan line to scan line Data quantization 8-bits (256 discrete levels) Number of video samples/scan line 699 Roll compensation +/-15 degrees Scan mirror 45-degree rotating mirror 4.2.1.1 Tolerance The NS001 channels were designed for noise-equivalent reflectance differences for the channels, represented by the radiometric sensitivity [NE(delta P) %; NE(delta T) K] shown in Section 4.2.1. 4.2.2 Frequency of Calibration An integrating sphere and two controllable thermal blackbodies are integral to the NS001 scanner. Each is viewed once during a complete revolution of the scan mirror. The two thermal blackbodies are principally used to span the recorded thermal image thereby providing a scaling factor for the measured data. The surface of blackbody number 2 is also used to provide the tare value (darkest object viewed per sweep) for the seven nonthermal detectors. Tare value is artificially set above zero counts (e.g., 8-10 counts) to compensate for any system drift. For BOREAS, one of the blackbodies is used for the internal lamp offset. The average of the two blackbodies is used for the scene offset. 4.2.3 Other Calibration Information 4.2.3.1 Reflective Band Calibration The BB2 View is used for the internal source offset; i.e., the gain is calculated in effect as: Gain = (Ref. Lamp View - BB2 View) / Ref. Lamp Spectral Radiance The reference lamp spectral radiance is determined by preseason calibration relative to the integrating sphere. The apparent scene spectral radiance can then be calculated as: (pixel value - (BB1 View + BB2 View) / 2) / Gain 4.2.3.2 Thermal Band Calibration GSFC Gain (G), Offset (O), as found in the header summary file(s), are calculated as follows: a) Calculate black body radiances, Lw(mW/cm2-sr-um) (assume emissivity=1) for BB1 and BB2 temperatures T(K), e.g.: Lw,BB1 = [K1 / (exp(K2/Tbb1)-1)] K1 = 60.705 mW/(cm2-sr-µm) K2 = 1258.39 K K1, K2 were "best fit" parameters for the temperature range of 273-323 K using the 8/87 NS001 spectral data and the Planck equation. b) G = [(BB2 View - BB1 View) / (Lw,BB2 - Lw,BB1)] (DN-cm2-sr-µm)/m2 O = BB1 View - G * Lw,BB1 (DN) Target Radiance (Lw) can then be calculated as: (pixel value - O) / G and at-sensor apparent temperature as: T = [K2 / (ln(K1/Lw + 1)] 5. Data Acquisition Methods As part of the BOREAS Staff Science data collection effort, the ARC Medium Altitude Aircraft Branch collected and processed eight-band NS001 TMS MSS data to BOREAS Level-0 products. The NS001 was flown on NASA's C-130 aircraft during BOREAS (see the BOREAS Experiment Plan for flight pattern details and objectives). Maintenance and operation of the instrument are the responsibility of ARC. The C-130 Experimenter's Handbook (supplemental) produced by the Medium Altitude Aircraft Branch at ARC provides a description of the instrument, calibration procedures, and data format. Data from the Level-0 tapes provided by ARC can be decoded based on the contents of the handbook. NS001 data may be intentionally overscanned; e.g., operated at some integral multiple of the desired scan rate and then subsampled in preprocessing. The subsampling factor is reported under the label "demagnification factor." 6. Observations 6.1 Data Notes The top portion of the ASCII header file in each Level-2 NS001 image product indicates that the band 8 data are 'Scaled Reflectance' when in fact they are 'Scaled Temperatures.' 6.2 Field Notes Flight summary reports and verbal records on video tapes are available for the BOREAS NS001 data. See related data sets, Section 1.6. 7. Data Description 7.1 Spatial Characteristics The BOREAS Level-2 NS001 TMS images cover portions of the Northern Study Area (NSA) and the Southern Study Area (SSA). 7.1.1 Spatial Coverage The geographic orientation of each image depends on the direction of the aircraft line of flight. Pixels and lines progress left to right and top to bottom so pixel n, line n is in the lower right-hand corner of each scene. 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 Typical altitudes for BOREAS were around 5,000 m, producing a 12.5-m pixel at nadir given the NS001's 2.5-mrad IFOV. 7.1.4 Projection The BOREAS Level-2 NS001 images are stored in their original data collection frame with increasing pixel sizes from nadir to the scanning extremes based on the scan angle. 7.1.5 Grid Description The BOREAS Level-2 NS001 images are stored in their original data collection frame with increasing pixel sizes from nadir to the scanning extremes based on the scan angle. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage The Level-2 NS001 images were acquired during 5 days from 19-Apr-1994 to 16-Sep- 1994. 7.2.2 Temporal Coverage Map Date Study Area ----------- ---------- 19-Apr-1994 SSA 07-Jun-1994 NSA 21-Jul-1994 SSA 08-Aug-1994 NSA 16-Sep-1994 SSA 7.2.3 Temporal Resolution Date Start Time End Time Number of images ----------- ---------- -------- ---------------- 19-Apr-1994 19:29 20:59 10 07-Jun-1994 18:14 19:18 9 21-Jul-1994 15:46 17:31 10 08-Aug-1994 14:32 15:13 7 16-Sep-1994 18:11 19:39 10 7.3 Data Characteristics 7.3.1 Parameter/Variable Scaled Reflectance (Bands 1 to 7) Scaled Surface Temperature (Band 8) Housekeeping data (Bands 1 to 8) Relative X coordinate Relative Y coordinate Scaled View zenith Scaled View Azimuth 7.3.2 Variable Description/Definition Scaled Reflectance The ratio of reflected radiant energy from the target to the incident radiant energy at the time of data collection in the specific NS001 wavelength regions. Scaled Surface Temperature The derived surface temperature at the time of data collection in the specific NS001 thermal infrared wavelength regions. Housekeeping data Housekeeping information extracted from the raw image files: one line of ASCII data per image line. Contains radiance per count calibration value, scan line number, blackbody counts, blackbody temperatures, scan speed, GMT, air temperature, channel number, blackbody radiance counts, reference lamp voltage, reference lamp current, reference lamp state, reference lamp radiance count, precision radiation thermometer value. Relative X coordinate The X coordinate of the center of the image pixel in relation to the arbitrarily selected origin. The trend of the X coordinates of the pixels is dependent on the direction of flight of the aircraft. The X, Y coordinate system, starts with the nadir pixel location of image line 1 for all flight lines positioned near the origin (0,0) and progresses based on the direction of flight. The flight direction refers to the angle of the flight path relative to magnetic North with North as 0 or 360 degrees, East as 90, South as 180, and West as 270 degrees. For example, the X coordinates for an idealized flight line in the direction of 180 degrees (South) would be increasingly positive to the left of the flight line and increasingly negative to the right of the flight line with the X coordinate for the nadir pixel being approximately 0 (zero). Relative Y coordinate The Y coordinate of the center of the image pixel in relation to the arbitrarily selected origin. The trend of the Y coordinates of the pixels is dependent on the direction of flight of the aircraft. The X, Y coordinate system, starts with the nadir pixel location of image line 1 for all flight lines positioned near the origin (0,0) and progresses based on the direction of flight. The flight direction refers to the angle of the flight path relative to magnetic North with North as 0 or 360 degrees, East as 90, South as 180, and West as 270 degrees. For example, the Y coordinates for an idealized flight line in the direction of 90 degrees (East) would be increasingly positive to the left of the flight line and increasingly negative to the right of the flight line with the Y coordinate for the nadir pixel being approximately 0 (zero). Scaled View zenith The scaled value of the target-centered view zenith angle (complement of elevation angle). The view zenith indicates the zenith angle at which the radiant energy was traveling when detected by the sensor. The view zenith angle increases from 0 (straight up) to 90 degrees at the horizon. Scaled View Azimuth The scaled value of the target-centered view azimuth angle. The view azimuth angle indicates the direction in which the radiant energy was traveling when detected by the sensor. The view azimuth angle increases from 0 to 360 degrees with North as 0 or 360 degrees, East as 90, South as 180, and West as 270 degrees. 7.3.3 Unit of Measurement Scaled Reflectance - Unitless. Look near the end of the ASCII header file for scaling factors. Scaled Surface Temperature - Temperature in degrees Celsius. Look near the end of the ASCII header file for scaling factors. Relative X coordinate - Tenths of meters Relative Y coordinate - Tenths of meters Scaled View zenith - Tenths of degrees Scaled View Azimuth - Tenths of degrees 7.3.4 Data Source The values stored in the listed parameters were extracted from the Level-0 NS001 files provided to BOREAS and processed to reflectance or surface temperature. The reflectance and surface temperature values are derived from the Level-0 data combined with the calibration parameters, so the at-sensor radiance data (Level- 1) were an intermediate product. View angle values are the result of calibration and processing of the raw NS001 data by NS001 personnel. The relative X and Y coordinates were derived in a joint effort between BORIS and NS001 personnel. 7.3.5 Data Range Scaled Reflectance and Surface Temperature Dependent on the particular MAS band of interest due to the wavelength region covered and the scaling factor listed near the end of the ASCII header file. Relative X coordinate Dependent on the direction of flight with an absolute minimum of -2,147,483,648 and absolute maximum of 2,147,483,647 for a 32-bit integer field. Relative Y coordinate Dependent on the direction of flight with an absolute minimum of -2,147,483,648 and absolute maximum of 2,147,483,647 for a 32-bit integer field. Scaled View zenith Minimum - 0 Maximum - 900 Scaled View Azimuth Minimum - 0 Maximum - 3599 7.4 Sample Data Record Not applicable to image data. 8. Data Organization 8.1 Data Granularity The smallest unit of data for Level-2 NS001 images is a single image. 8.2 Data Format(s) 8.2.1 Uncompressed Data Files A single NS001 Level-2 image product consists of 21 files: File 1: An ASCII header file that containing information relating to the mission, location, acquisition time, sensor parameters, aircraft location and attitude, and radiometric calibration parameters. Files 2 - 8: Bands 1 to 7 stored as 16-bit integer values in scaled reflectance (low-order byte first). Look near the end of the ASCII header file for scaling factors. File 9: Band 8 stored as 16-bit integer values in scaled degrees Celsius (low- order byte first). Look near the end of the ASCII header file for scaling factors. Files 10 - 17: ASCII files containing the unpacked housekeeping information. File 18: Relative X coordinates stored as 32-bit integer values in meters (low-order byte first). File 19: Relative Y coordinates stored as 32-bit integer values in meters (low-order byte first). File 20: Scaled-view zenith values stored as 16-bit integer values in tenths of degrees (low-order byte first). File 21: Scaled-view azimuth values stored as 16-bit integer values in tenths of degrees (low-order byte first). The geographic orientation of each scene depends on the direction of the aircraft line of flight. Pixels and lines progress left to right and top to bottom so pixel n, line n is in the lower right-hand corner of each scene. All image files contain a variable number of fixed-length records. The ASCII header files are 80 bytes in length. All binary files for a given flight contain the same number of records. The number of binary records in a flight varies depending on the length of that flight line. Each binary data record in all flights represents 699 image pixels. Therefore, the image and view angle file records contain 699*2 = 1398 bytes, and the relative X and Y coordinate files contain 699*4 = 2796 bytes. 8.2.2 Compressed CD-ROM Files On the BOREAS CD-ROMs, the ASCII header file for each image is stored as ASCII text; however, files 2 to 21 have been compressed with the GNUzip (Gzip) compression program (file name *.gz). These data have been compressed using Gzip version 1.2.4 and the high compression (-9) option (Copyright (C) 1992- 1993, Jean-loup Gailly). Gzip uses the Lempel-Ziv algorithm (Welch, 1994) used in the zip and PKZIP programs. The compressed files may be uncompressed using Gzip (-d option) or Gunzip. Gzip is available from many Websites (for example, FTP site prep.ai.mit.edu/pub/gnu/gzip-*.*) for a variety of operating systems in both executable and source code form. Versions of the decompression software for various systems are included on the CD-ROMs. 9. Data Manipulations 9.1 Formulae 9.1.1 Derivation Techniques and Algorithms The atmospheric correction algorithm, Imagecor, applied to the NS001 Level-0 data is fully documented in Wrigley et al. (1992), which has since been modified to include water vapor and to remove path thermal emission for thermal channels. Imagecor was developed by Robert Wrigley and Robert Slye for the atmospheric correction of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) data and uses a simple atmospheric model with a modified single-scattering approximation, which permits full image scenes to be processed relatively quickly. Water vapor corrections are based on modeled water vapor transmittance output by 6S combined with water vapor transmittance derived from 940-nm channel sunphotometer data. This transmittance and the spectral response function of the sunphotometer channel were used to determine the equivalent water vapor column content. Imagecor then uses this content to estimate the transmittance across the scene. The thermal channel was corrected by using MODTRAN to model path emission and transmittance at 12 equally spaced angles across the scene and interpolating the path emission between these points. Derivation of the relative X and Y coordinates starts with determining the relative positions of the nadir pixel in each image line. The nadir pixel coordinates are defined to proceed relative to an arbitrary starting X,Y location. Nadir X,Y coordinates are derived as a function of the following parameters: • Instantaneous velocities X, Y, and Z from the C130 navigation data. • Tracking (actual direction aircraft is pointing) values derived as a function of true heading and drift. To determine nadir pixel tracking, the 1- Hz drift values and 30-Hz true heading values are interpolated to nadir pixel values. Nadir pixel drift is added to the nadir true heading values to obtain nadir pixel tracking values. Note that drift may be a positive or negative value. The calculations used to derive relative X and Y coordinates of the nadir pixels are: X0 = First (earlier) nadir X location X1 = Succeeding nadir X location Y0 = First (earlier) nadir Y location Y1 = Succeeding nadir Y location DTime = Time1 - Time0 [Delta time stamps between succeeding nadir pixels] TH0, TH1 = True heading at succeeding nadir pixel. Dr0, Dr1 = Drift values at succeeding nadir pixels Tr0, Tr1 = Tracking at succeeding nadir pixels VX,VY,VZ = Global Positioning system (GPS) velocities in an X, Y and Z GPS reference system Sp0, Sp1 = Ground speed [square root ((VX*VX) + (VY*VY) + (VZ*VZ))] V0x = SP0 * cos(TH0 + Dr0) [X Velocity at Time0] V1x = SP1 * cos(TH1 + Dr1) [X Velocity at Time1] V0y = SP1 * sin(TH0 + Dr0) [Y Velocity at Time0] V1y = SP1 * sin(TH1 + Dr1) [Y Velocity at Time1] AVEV01X = (V0x + V1x) / 2.0 [Average X velocity between Time0 and Time1] AVEV01Y = (V0y + V1y) / 2.0 [Average Y velocity between Time0 and Time1] X = X0 + (AVE01X * DTime) [Succeeding nadir X coordinate] Y = Y0 + (AVE01Y * Dtime) [Succeeding nadir Y coordinate] The X and Y values along each scan line are projected from the center pixel in both directions where AngleIncr = 100 degrees/699 pixels x0 = center pixel x coordinate y0 = center pixel y coordinate pitch = pitch of the aircraft interpolated to the center pixel time from the c130 navigation data ScanAngle = fabs(AngleIncr * (pixel)) XCoords[pixel] = x0 + alt*tan(pitch)*sin(head) - alt/cos(pitch) * (tan(ScanAngle)) * cos(head) YCoords[pixel] = y0 + alt*tan(pitch)*cos(head) + alt/cos(pitch) * (tan(ScanAngle)) * sin(head) 9.2 Data Processing Sequence 9.2.1 Processing Steps BORIS and ARC personnel created Level-2 NS001 image products in an iterative procedure as follows: 1) Extract approximate center pixel times from NS001 image files. 2) Extract 30-hz (heading, pitch, roll) and 1-hz (alt, drift, xyz velocities) data from navigation data files. 3) Interpolate navigation data to center pixel times and place into .xy file. 4) Create two image bands, an X and a Y, which contain a coordinate for each of the 699 pixels in each scan line. 5) Unpack the seven reflectance and one temperature bands into separate files. The flight lines were then sent to NASA ARC for atmospheric correction processing, which involved: 1) Reading the data tape and exporting the image data to files with system- specific byte order. 2) Downloading the radiosonde and sunphotometer data from BORIS. 3) Modeling the path transmittance and path radiative emission for the thermal channel using a MODTRAN and modeling the path water vapor column concentration and downwelling irradiance using the 6S for visible and near- and mid-infrared channels. 4) Processing the image data to reflectance or surface temperature using Imagecor. 5) Generating a header file for each of the NS001 flight lines. 6) For each flight line, writing to tape each header file and Level-2 image data, with housekeeping, X and Y, and zenith and azimuth data. 7) Sending the data tape to BORIS. BORIS Staff performed the following final steps: 1) Extracted pertinent header information from each image. 2) Loaded inventory information in the relational data base. 3) Reviewed random files for content. 9.2.2 Processing Changes None. 9.3 Calculations 9.3.1 Special Corrections/Adjustments None. 9.3.2 Calculated Variables See Section 9.1.1. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error The NS001 data are calibrated in-flight by reference to the NS001 internal integrating sphere source. Apparent instabilities in this source or its monitoring circuitry, which are not fully understood, are the principal limiting factors in the absolute calibration of NS001 data. Uncertainties caused solely by this behavior reached 25% in 1987, though more typically they are expected to be less than 15%. Other identified error sources at the 1-2% level for typical signals include dark current drift along the scan line, hysteresis-like sensitivity changes along the scan line, random noise, scan-speed-induced errors, and nonlinearity of radiance with wavelength. Channel 7 (2.08-2.35 µm) shows a number of peculiarities that are hysteresis- like, including a change in the apparent dark current drift along scan with scene brightness and a drop in sensitivity in scanning across a bright target of an estimated 8% over the total 100-degree scan angle. Polarization sensitivity of the NS001 was such that for typical atmospheric conditions errors in channel 1 (0.45-0.52 µm), radiances would be up to +/-10% and vary with scan angle; this progressively decreases with increasing wavelength (Markham and Ahmad, 1990). In addition to these errors, the Level-2 errors are dependent on the accuracy of the aerosol optical depth measurements used in the atmospheric correction processing. Errors caused by using a single-scattering approximation should be minimal because the BOREAS optical depths were low (met the single-scattering requirement). 10.2 Quality Assessment 10.2.1 Data Validation by Source Spectral errors could arise from image-wide signal-to-noise ratio, saturation, cross-talk, spikes, or response normalization caused by change in gain. NS001 Level-2 pixel data agreed well with helicopter-acquired Barnes Modular Multispectral Radiometer (MMR, BOREAS PI: Charles Walthall) data for the BOREAS primary study sites, for the flight lines that coincided the primary sites. With similar geometric and site condition inputs, both 6S and MODTRAN modeled reflectances also were in close agreement to the Imagecor results. BORIS personnel used the relative X and Y coordinate files to perform forward mapping of several NS001 images as a check of the calculations. Visual assessment of the forward-mapped images showed the relative corrections to significantly remove distortions from scan angle and aircraft motion. Overlay of the forward-mapped images on a Landsat TM image showed the features to be in good alignment after nominal shifting and rotation of the image without further stretching or distortion. 10.2.2 Confidence Level/Accuracy Judgment System optical focus is continually monitored by close observation of the apparent sharpness and resolution of objects appearing in scenes after data processing. Although this is somewhat subjective, the approach has proved to be a viable alternative compared to the classical resolution measurement method. The latter method requires removing the scanner system from the C-130 airplane with subsequent setup. This is not a practical option during the flying/deployment portion of the year. However, any observed focus degradation would be corrected by focus adjustment. 10.2.3 Measurement Error for Parameters The Noise Equivalent Spectral Radiance for the channels ranges from 0.08 to 2.77 microwatts per square cm. Uncertainties caused by the behavior of the internal integrating sphere reached 25% in 1987, though more typically they are expected to be less than 15%. 10.2.4 Additional Quality Assessments None. 10.2.5 Data Verification by Data Center None other than reviewing the values extracted from the tape files and loaded in the data base. 11. Notes 11.1 Limitations of the Data To date, the following discrepancies/problems have been noted in the data: Certain values in the header information, such as MEAN_FRAME_STATUS, MEAN_ and STDV_GSFC, and AMES_GAIN and OFFSETS, especially for bands 7 and 8, were outside the valid range for these parameters. Such values, when found, were entered into the BORIS data base as the number -99.0 or -999.0, depending on the data base field width. The problem appears to occur randomly. 11.2 Known Problems with the Data The top portion of the ASCII header file in each Level-2 NS001 image product indicates that the band 8 data are 'Scaled Reflectance' when in fact they are 'Scaled Temperatures.' 11.3 Usage Guidance The NS001 data are not geometrically corrected. The data contain both panoramic distortion, as a function of the 100-degree total field of view, as well as the other spatial perturbations induced by a moving aircraft. BORIS personnel used the relative X and Y coordinate files to perform forward mapping of several NS001 images as a check of the calculations. Visual assessment of the forward- mapped images showed the relative corrections to significantly remove distortions from scan angle and aircraft motion. Overlay of the forward-mapped images on a Landsat TM image showed the features to be in good alignment after nominal shifting and rotation of the image without further stretching or distortion. Before uncompressing the Gzip files on CD-ROM, be sure that you have enough disk space to hold the uncompressed data files. Then use the appropriate decompression program provided on the CD-ROM for your specific system. 11.4 Other Relevant Information Two in-flight adjustments are made that affect the radiometric calibration of the reflective channels. The primary adjustment is to the postamplifier gain of each channel. This is adjusted by means of a channel-specific potentiometer before and between data acquisitions to optimize the spread of the data across the range of the A/D converter (8 bits). The gain settings are continuously variable and are not directly recorded in the data; they are inferred from changes in the instrument response to the integrating sphere. The second adjustment is for scan speed, which is adjusted between 10 and 85 scans per second to maintain contiguous scan lines, or some multiple of contiguous if contiguity is not maintainable at the altitude required for data collection. Typical altitudes for BOREAS in 1994 were 5,000 m, which produced 12.5-m pixels at nadir given the NS001's 2.5-mrad IFOV. 12. Application of the Data Set These data could be used to study the reflectance or temperature characteristics of various surface features. 13. Future Modifications and Plans None. The NS001 instrument was decommissioned in October 1995. 14. Software 14.1 Software Description BORIS Staff developed software and command procedures for: 1) Extracting header information from Level-0 NS001 TMS images on tape and writing it to ASCII files on disk. 2) Reading the ASCII disk file and logging the Level-0 NS001 image products into the Oracle data base tables. The atmospheric correction software, Imagecor, was written in the C language, is operational on Sun Microsystems Solaris systems, and has few hardware dependencies. 14.2 Software Access The software is written in the C language and is operational on VAX 6410 and MicroVAX 3100 systems at GSFC. The primary dependencies in the software are the tape Input/Output (I/O) library and the Oracle data base utility routines. For information on Imagecor, contact one of the individuals listed in Section 2. 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 (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 BOREAS Level-2 NS001 TMS data can be made available on 8-mm, Digital Archive Tape (DAT), or 9-track tapes at 6250 or 1600 bytes Per Inch (BPI). 16.2 Film Products Color aerial photographs and video records were made during data collection. The video record includes aircraft crew cabin intercom conversations and an audible tone that was initiated each time the sensor was triggered. The BOREAS data base contains an inventory of available BOREAS aircraft flight documentation, such as flight logs, video tapes, and photographs. 16.3 Other Products None. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation Airborne Instrumentation Research Project - Flight Summary Reports for Flight No. 94-004-09 to 94-009-09 or April 16, 1994 to September 19, 1994. NASA Ames Research Center. Airborne Missions and Applications Division. Moffett Field. CA. 94035. NASA. 1990. C-130 Earth Resources Aircraft Experimenter's Handbook. National Aeronautics and Space Administration. Ames Research Center. Moffett Field, CA. Operations Manual - NS001 Multispectral Scanner. 1977. Lyndon B. Johnson Space Flight Center. Document # JSC 12715. Welch, T.A. 1984, A Technique for High Performance Data Compression, IEEE Computer, Vol. 17, No. 6, pp. 8 - 19. 17.2 Journal Articles and Study Reports Ahmad, S.P. and B.L. Markam. 1992. Radiometric Calibration of a Polarization- Sensitive Sensor. J. Geophys. Res. Vol. 97:18,815 -18,827. Gordon, H.R., D.K. Clark, J.W. Brown, O.B. Brown, R.H. Evans, and W.W. Broenkow. 1983: Phytoplankton pigment concentrations in the Middle Atlantic Bight: Comparison of ship determinations and CZCS estimates. Appl. Opt., 22, 20-36. Hall, F.G., P.J. Sellers, I. McPherson, R.D. Kelly, S. Verma, B. Markham, B. Blad, J. Wang, and D.E. Strebel. 1989. FIFE: Analysis and Results - A Review, Adv. Space Res. 9(7):275-293. Markam, B.L. and S.P. Ahmad. 1990. Radiometric properties of the NS001 Thematic Mapper Simulator aircraft multispectral scanner. Remote Sens. Environ. 34:133- 149. Markam, B.L., F.M. Wood, Jr., and S.P. Ahmad. 1988. Radiometric calibration of the reflective bands of NS001-Thematic Mapper Simulator and Modular Multispectral Radiometers. In: Recent Advances in Sensors, Radiometry and Data Processing for Remote Sensing. Proc. SPIE Vol. 924, Bellingham, WA. pp. 96-108. Newcomer, J.A., S.J. Goetz, D.E. Strebel, and F.G. Hall. 1989. Image processing software for providing radiometric inputs to land surface climatology models. IGARSS '89. 12th Can. Symp. on Remote Sensing, p. 1779-1782. Richard, R.R., R.F. Merkel, and G.R. Meeks. 1978. NS001MS - Landsat-D Thematic Mapper Band Aircraft Scanner. In: Proc. 12th Int. Sym. Remote Sens. Environ., pp. 719-728. 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 (OPS DOC 94). Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 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. Strebel, D.E., S.J. Goetz, and F.G. Hall. 1987. Atmospheric correction of NS001 data and extraction of multiple angle reflectance data sets. In: Proc. 21st Int. Sym. Remote Sens. Environ. ERIM. Ann Arbor, MI, pp. 939-948. Wrigley, R.C., M.A. Spanner, R.E. Slye, R.F. Puseschel, and H.R. Aggarwal. 1992. Atmospheric Correction of Remotely Sensed Image Data by a Simplified Model. Journal of Geophysical Research 97(D17):18797-18814. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List of Acronyms 6S - Second simulation of the Satellite Signal in the Solar Spectrum ARC - Ames Research Center ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System BPI - Bytes per inch CCRS - Canada Centre for Remote Sensing CCT - Computer Compatible Tape CD-ROM - Compact Disk-Read-Only Memory DAAC - Distributed Active Archive Center DAT - Digital Archive Tape EOS - Earth Observing System EOSDIS - EOS Data and Information System ERTS - Earth Resources Technology Satellite FIFE - First ISLSCP Field Experiment fPAR - Fraction of Photosynthetically Absorbed Radiation GICS - Geocoded Image Correction System GMT - Greenwich Mean Time GPS - Globa; Positioning Time GSFC - Goddard Space Flight Center Gzip - GNU zip IFOV - Instantaneous Field of View Imagecor- Image Atmospheric Correction INS - Inertial Navigation System I/O - Input/Output ISLSCP - International Satellite Land Surface Climatology Project LAI - Leaf Area Index MAS - MODIS Airborne simulator MMR - Modular Multispectral Radiometer MODIS - Moderate-Resolution Imaging Spectrometer MODTRAN - Moderate Resolution Model of LOWTRAN 7 MSS - Multispectral Scanner NASA - National Aeronautics and Space Administration NSA - Northern Study Area ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park RSS - Remote Sensing Science SSA - Southern Study Area TM - Thematic Mapper TMS - Thematic Mapper Simulator URL - Uniform Resource Locator 20. Document Information 20.1 Document Revision Date(s) Written: 09-Jun-1995 Last Updated: 07-May-1998 20.2 Document Review Date(s) BORIS Review: 24-Apr-1998 Science Review: 20.3 Document ID 20.4 Citation The Level-2 NS001 images were processed at NASA ARC under BOREAS investigation Remote Sensing Science (RSS)-12, with Michael Spanner as Principal Investigator. If appropriate, the references cited in Section 17 should be used. 20.5 Document Curator 20.6 Document URL C-130 NS001 NS001 TMS THEMATIC MAPPER SIMULATOR TMS EMITTED RADIATION REFLECTED RADIATION NS001_L2.doc 05/26/98