FIRE_ACE_AMPR Readme NOTE: These are preliminary datasets; they are not the final versions. The current dataset is preliminary quality controlled and calibrated, valid October 1998, version 1.0. 1.0 Introduction This file contains information about the data provided by the Advanced Microwave Precipitation Radiometer (AMPR) flown onboard the ER2 aircraft during the FIRE ACE field campaign. It includes implemmentation of the sample READ software. This data set is available through the Langley Atmospheric Sciences Data Center as: FIRE_ACE_AMPR Each granule contains one flight of data taken at 3 second intervals and several images in 'gif' format. The images represent 15 minutes of data. The data consists of Brightness Temperatures at 4 frequencies (10.7, 19.36, 37.1, 85.5 Ghz) as well as navigation information. Additional information about the AMPR dataset and images can be obtained at http://wwwghcc.msfc.nasa.gov/ampr/ This Readme file includes four other sections: Section 2.0 - Instrument description Section 3.0 - Data quality Section 4.0 - Data set information Section 5.0 - Read software description and implementation If there are questions about using the FIRE_ACE_AMPR sample read software, please contact the Langley User and Data Services (UDS) office at: Langley DAAC User and Data Services Office 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 Instrument Description The Advanced Microwave Precipitation Radiometer (AMPR) is a total power scanning multifrequency radiometer which collects data at 10.7, 19.35, 37.1, and 85.5 GHz. The AMPR is composed of two adjacent antenna systems with one large scanning mirror accommodating both systems. One antenna system was designed to use a copy of the SSM/I feedhorn for the three higher frequencies. The second antenna system collects data at 10.7 GHz using a feedhorn designed by the Georgia Tech Research Institute (GTRI). The AMPR is currently configured to fly aboard the high altitude ER-2 aircraft. The ground spatial resolution at nadir with zero degrees pitch and roll, and 20 km altitude are: 2.8 km at 10.7 GHz (approximate) 2.8 km at 19.35 GHz 1.5 km at 37.1 GHz 0.6 km at 85.5 GHz The AMPR calibrates with external cold and warm loads after every fourth data (surface) scan. A total calibration sequence or a total data scan are each performed in a three second time period. The AMPR scanner sweeps through a total 90 degree (+/- 45 degrees from nadir) data scan collecting a sample for each channel every 1.8 degrees for a total of 50 samples per channel. Based upon an aircraft altitude of 20 km and an aircraft speed of 200 m/s, this scan rate will yield contiguous footprints for the 85.5 GHz channel within a 40 km wide swath. The three other channels will be oversampled by the factors given in Table I. Also listed in Table I are other performance characteristics of the radiometer. The feedhorns have been aligned such that full vertical polarization is 45 degrees left of nadir and full horizontal polarization is 45 degrees right of nadir. An equal mix of polarization occur at nadir. A more thorough discussion of the instrument may be found in Spencer, et al., 1994, Journal of Atmospheric and Oceanic Technology, Vol. 11, No. 4, pp.849-857. Table I. AMPR Instrument Characteristics IF 3dB Mainbeam Cross Frequency Bandwidth Beamwidth Oversampling Efficiency Polarization --------- --------- --------- ------------ ---------- ------------ 85.5 GHz 1400 MHz 1.8 deg 1.0x 93.2% 1.4% 37.1 GHz 900 MHz 4.2 deg 2.3x 98.8% 0.4% 19.35 GHz 240 MHz 8.0 deg 4.4x 98.7% 1.6% 10.7 GHz 100 MHz 8.0 deg 4.4x 97.8% 0.2% 3.0 Data Quality NOTE: These are preliminary datasets; they are not the final versions. The current dataset is preliminary quality controlled and calibrated, valid October 1998, version 1.0. The Scientists feel the brightness temperature and navigation data are of good quality, but they have yet to run it through a number of quality assurance checks to put final approval on it. They suggest using the data with this in mind, although please contact Ms. Robbie Hood or Mr. Frank LaFontaine (contact information listed below) at any time when you wish to do quantitative studies with the data. They may have other important information or suggestions. The data have been basically calibrated but the brightness temperatures are not yet fully quality assured. The pixel navigation is preliminary; fairly precise but not yet fully quality assured. Some flights may be missing navigation, possible recovery from other navigation recorders may be possible and will be applied, if useable, in the final (future) data set. 4.0 FIRE_ACE_AMPR Data Set Information Each file contains one flight of data in ASCII format. A -32768 indicates a flagged value, a -999.99 indicates missing values. Element #1 has full vertical polarization, element #50 has full horizontal polarization. Surface resolutions at nadir with zero degrees pitch and roll, and 20 km altitude are: 2.8 km at 10.7 GHz (approximate) 2.8 km at 19.35 GHz 1.5 km at 37.1 GHz 0.6 km at 85.5 GHz 4.1 File Naming Convention: The FIRE_ACE_AMPR data granules are prefixed with "fire_ace_ampr_" to indicate they belong to this data set. A seven digit designation follows the prefix and it indicates the year and julian day of flight. Example filename: fire_ace_ampr_1998130 AMPR data taken May 10, 1998 4.2 Parameter Definitions The data include day, time, navigation, and 50 brightness temperatures for each channel per scan of the instrument. Specific parameters are given below. Parameter Description (range; units) iscan Scan number (1-maximum number of records) year Year (1998) julian_day Julian day of year (130-159) hour Hour (0-23; UTC) minute Minute (0-59; UTC) second Second (0-59; UTC) igbp GPS validity code (1=Good) gps_alt GPS Altitude of the ER2 (meters) gps_lat GPS Latitude of the ER2 (degrees) gps_lon GPS Longitude of the ER2 (degrees) er2_head Heading of the ER2 (0,360=North, clockwise) er2_pitch Pitch of the ER2 (+up) er2_roll Roll of the ER2 (+right) er2_grd Ground Speed of the ER2 (m/s) er2_air Air Speed of the ER2 (m/s) er2_balt Barometric Altitude of the ER2 (m) ins_lat INS Latitude (degrees) ins_lon INS Longitude (degrees) rms_noise(4) RMS noise for each channel (10.7, 19.35, 37.1, 85.5 GHz; K) tbs10(50) Brightness Temperature at 10.7 Ghz for each pixel (K) tbs19(50) Brightness Temperature at 19.35 Ghz for each pixel (K) tbs37(50) Brightness Temperature at 37.1 Ghz for each pixel (K) tbs85(50) Brightness Temperature at 85.5 Ghz for each pixel (K) pix_lat(50) Latitude for each pixel (degrees) pix_lon(50) Longitude for each pixel (degrees) CONTACTS FOR FIRE_ACE_AMPR DATA PRODUCT INFORMATION: Ms. Robbie Hood NASA / MSFC Global Hydrology and Climate Center (GHCC) 977 Explorer Blvd. Huntsville, AL 35806 USA E-mail: Robbie.Hood@msfc.nasa.gov Phone: (256) 922-5959 Fax: (256) 922-5723 Mr. Frank LaFontaine Raytheon ITSS Global Hydrology and Climate Center (GHCC) 977 Explorer Blvd. Huntsville, AL 35806 USA E-mail: Frank.LaFontaine@msfc.nasa.gov Phone: (256) 922-5796 Fax: (256) 922-5723 5.0 Read Software Currently, there is one sample read program which works with the FIRE_ACE_AMPR data set, read_fire_ace_ampr.f. It is written in Fortran 77. This program has been tested on the following computers and operating systems: Computer Operating System ------------------- ---------------- Sun Sparc Solaris 2.6 SGI Origin 2000 IRIX 6.4 HP 9000/735 HP-UX 10.10 This program is written as an example of how to read in the AMPR data. As delivered, it reads in and writes to the screen the sample data for every 500th scan of the instrument. 5.1 Implementing the READ Software To compile the program, use the command for the Fortran 77 compiler. The command may vary slightly among operating systems. On most systems the command is: % f77 -o read_ampr read_fire_ace_ampr.f If the appropriate compile command is not found on your system, check to be sure that your PATH environment variable includes the directory that contains the compiler or specify the entire path to the compiler in your command. This compile command creates an executable program file named read_ampr. 5.2 Executing the AMPR READ Software To execute the AMPR read program: % read_ampr The user is prompted by the program to enter the filename of interest. 5.2 Sample output from executing the AMPR READ Software The read_fire_ace_ampr.f f77 program can be used to read any of the AMPR data files. The following is a sample session showing compilation and execution of the program. % f77 -o read_ampr read_fire_ace_ampr.f read_fire_ace_ampr.f: MAIN read_ampr_data: % read_ampr Enter the AMPR file name fire_ace_ampr_1998130 Scan: 500 Date: 1998130 Time(UTC): 15:18:19 Tb10: 269.72 Tb19: 269.00 Tb37: 269.91 Tb85: 267.41 Lat: 35.91068 Lon: -118.01702 Scan: 1000 Date: 1998130 Time(UTC): 15:43:40 Tb10: 267.45 Tb19: 265.97 Tb37: 266.97 Tb85: 264.32 Lat: 36.14126 Lon: -118.06417 Scan: 1500 Date: 1998130 Time(UTC): 16: 9: 2 Tb10: 278.97 Tb19: 273.58 Tb37: 275.14 Tb85: 277.07 Lat: 33.86510 Lon: -117.71359 Scan: 2000 Date: 1998130 Time(UTC): 16:34:24 Tb10: 275.23 Tb19: 276.16 Tb37: 274.46 Tb85: 271.88 Lat: 35.60397 Lon: -118.17465 Scan: 2500 Date: 1998130 Time(UTC): 16:59:57 Tb10: 268.71 Tb19: 271.66 Tb37: 271.25 Tb85: 273.20 Lat: 34.93702 Lon: -117.82162 All data read from file fire_ace_ampr_1998130 Total number of Scans ... 2801