Langley DAAC Version Number: LD_008_006_002_00_00_0_19990415 FIRE_ACE_ER2_MIR Readme 1.0 Introduction ---------------- This file contains information about the data provided by the Millimeter-wave Imaging Radiometer (MIR) flown onboard the ER2 aircraft during the FIRE-ACE field campaign. It includes implementation of the sample READ software. This data set is available through the Langley Atmospheric Sciences Data Center as: FIRE_ACE_ER2_MIR Each granule contains one flight of data taken at 3 second intervals. The data consists of Brightness Temperatures at 7 frequencies (89, 150, 183.3 +/-1, 183.3 +/-3, 183.3 +/-7, 220, 340 Ghz) as well as navigation information. This Readme file includes four other sections: Section 2.0 - Instrument description Section 3.0 - Data set information Section 4.0 - Read software description and implementation If there are questions about using the FIRE_ACE_ER2_MIR 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 Millimeter-wave Imaging Radiometer (MIR) as configured for the FIRE-ACE experiment is a seven-channel scanning radiometer with channels at 89, 150, 183 +/-1, 183 +/-3, 183 +/-7, 220, and 340 GHz. The nominal antenna beamwidth for each channel is 3.5 deg., and the swath scanned is 100 deg. The 340 GHz channel is a new channel just installed in March 1998. The MIR has primarily been used for the study and development of techniques for retrieving water vapor distributions. More recent studies have focused on the application of the MIR frequencies for the measurement of clouds and the effects of clouds on the retrieval of atmospheric water vapor. The FIRE-ACE experiment is an excellent opportunity for extending the data set for such analyses. Objectives The frequency ensemble of the MIR, along with measurements from other instrumentation, are useful for inferring surface properties, cloud coverage, and water vapor distributions. The higher frequency channels, i.e., 183 GHz and higher, are sensitive to the presence of cirrus clouds. Scattering from cloud ice is observed as depressions in brightness temperatures. Absorption by atmospheric water vapor obscures the surface. The 89 and 150 GHz channels respond to fluctuation in the surface emissivity. These channels also respond to water clouds. In dry conditions like those observed during the FIRE-ACE campaign, the 220 GHz channel also displays significant response to surface conditions and cloud absorption. The measured temperatures at these channels are a function of the surface albedo and path attenuation. The data set acquired will be used to study the scattering characteristics of ice clouds, the utility of the new 340 GHz channel and the interaction of surface characteristics and low level clouds detected in the atmospheric window channels. Another application of the MIR data set is the retrieval of surface albedo and columnar water vapor in the presence of clouds over ocean ice. Finer spatial resolution of sea ice distributions may be obtained using millimeter wave frequencies than using microwave frequencies. Instrument Performance The MIR instrument performed well throughout the FIRE-ACE experiment with a few exceptions. There were three data flights (on days 153, 154, and 155) during which the MIR exhibited a problem with the A/D boards resulting in about a 30% data loss. Example Results The browse image accompanying this data set, fire_ace_er2_mir_1998153_3.gif, shows MIR brightness temperatures from the seven-radiometric channels. The horizontal stripes in the image result from the problems associated with the A/D board. The 340 GHz channel is mislabeled as 325+/-3. Cloud Lidar System data shows a thin stratus layer starting at about 23:36; a layer of moderately thick cirrus is present at 23:40 and then the stratus cloud becomes significantly thicker. Low level clouds or fog over the ice are present in the CLS data in the time preceding the stratus layer, increasing the brightness temperatures of the window channels. A clearing in the fog occurs between 23:30 and 23:35. The 89, 150 and 220 GHz channels detect this clearing, indicated by a drop in brightness temperatures. Leads in the ice can be seen in the 89 and 150 GHz channels and in some cases the 220 GHz channels. 3.0 Data Set Information ------------------------ Each file contains one flight of data. The data are four-byte IEEE floating point values. The Brightness Temperatures should be within the range of 50 to 300K. Some data lie beyond these limits. Also, a 9999.0 indicates missing values. This version of the data set does not contain Brightness Temperatures for the 340Ghz channel. Calibration studies are currently underway and the data will be released at a later time. 3.1 File Naming Convention -------------------------- The FIRE_ACE_ER2_MIR data granules are prefixed with "fire_ace_er2_mir_" to indicate they belong to this data set. The year and julian day of the flight is next with the volume number following. Example filename: fire_ace_er2_mir_1998140_2 MIR data taken May 20, 1998, Volume 2 3.2 Parameter Definitions ------------------------- The data include day, time, navigation, and 57 brightness temperatures for each channel per scan of the instrument. Specific parameters are given below. Word Parameter Description(units;range) ----------------------------------------------------------------- 1 Record Number 2 Month Real time clock 3 Day Real time clock 4 Hour IRIG, UTC 5 Minute IRIG, UTC 6 Second IRIG, UTC 7 Julian Day Navigation 8 Hour Navigation, UTC 9 Minute Navigation, UTC 10 Second Navigation, UTC 11 Latitude Degrees 12 Longitude Degrees (-West, +East) 13 Air Temperature Degrees Celsius 14 Altitude Feet 15 Pitch Deg. (+ for nose down) 16 Roll Deg. (+ for roll right) 17 Heading Degrees 18- 26 HouseKeeping temp. Degrees Kelvin 27 Hot ave. temp. for this scan Degrees Kelvin 28 Cold ave. temp. for this scan Degrees Kelvin 29 Hot temp., 8-scan moving ave. Degrees Kelvin 30 Cold temp., 8-scan moving ave. Degrees Kelvin 31- 39 Hot ave., counts for this scan 40- 48 Cold ave., counts for this scan 49- 57 Hot counts, 8-scan moving ave. 58- 66 Cold counts, 8-scan moving ave. 67-123 57 Brightness Temp. at 89 GHz Deg. K; (50-300) 124-180 57 Brightness Temp. at 150 Deg. K; (50-300) 181-237 57 Brightness Temp. at 183.3 +/-1 Deg. K; (50-300) 238-394 57 Brightness Temp. at 183.3 +/-3 Deg. K; (50-300) 295-351 57 Brightness Temp. at 183.3 +/-7 Deg. K; (50-300) 352-408 57 Brightness Temp. at 220 Deg. K; (50-300) 409-465 57 Brightness Temp. at 340 Deg. K; (50-300) 3.3 Contact for Data Product Information ---------------------------------------- Dr. James Wang Goddard Space Flight Center M.S. 975.0 Greenbelt, Maryland 20771 USA Phone: (301) 614-5655 FAX: (301) 614-5558 E-mail: wang@sensor.gsfc.nasa.gov 4.0 Read Software ------------------ Currently, there is one sample read program which works with the FIRE_ACE_ER2_MIR data set, read_fire_ace_mir.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 Dec Alpha Digital UNIX 4.0A This program is an example of how to read the MIR data. As delivered, it reads all the data records in a file and writes to the screen the selected parameters for every 1000th scan of the instrument. 4.1 Implementing the READ Software ---------------------------------- *** Most f77 compilers *** 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_mir read_fire_ace_mir.f *** SGI f77 compiler *** If you are compiling on a SGI, you MUST use the following command: % f77 -o read_mir -bytereclen read_fire_ace_mir.f *** DecAlpha f77 compiler *** If you are compiling on a DecAlpha, you MUST remove the call to subroutine FLIP and use the following command: % f77 -o read_mir -assume byterecl read_fire_ace_mir.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_mir. 4.2 Executing the MIR READ Software ------------------------------------ To execute the MIR read program: % read_mir The user is prompted by the program to enter the filename of interest. 4.3 Sample output from executing the MIR READ Software ------------------------------------------------------ The read_fire_ace_mir.f f77 program can be used to read any of the MIR data files. The following is a sample session showing compilation and execution of the program. % f77 -o read_mir read_fire_ace_mir.f read_fire_ace_mir.f: MAIN read_fire_ace_mir: flip: % read_mir Enter Input Filename: fire_ace_mir_1998138.1 Opened Input File fire_ace_mir_1998138.1 1004 05 18 20:19:44 68.42 -151.95 19295.0 272.66 273.41 241.31 257.75 270.22 274.21 .00 2004 05 18 21:09:03 73.54 -160.48 19812.8 255.25 253.72 249.65 258.28 265.15 260.59 .00 3004 05 18 21:58:23 75.99 -156.63 19746.8 225.83 225.62 238.69 249.59 255.06 243.08 .00 4004 05 18 22:47:43 75.10 -165.65 19888.9 242.06 240.30 239.28 249.29 256.54 254.79 .00 5004 05 18 23:37:02 74.67 -166.12 20284.3 247.65 246.08 250.99 257.15 263.79 256.32 .00 6004 05 19 00:26:22 70.33 -154.55 20460.3 261.66 262.35 238.54 252.51 262.56 267.89 .00 7004 05 19 01:15:42 65.53 -148.31 8798.0 284.52 284.76 241.80 257.98 272.59 281.49 .00 Last Data Record 7199 Total Data Records 7194 STOP: 3 Updated April 19, 1999 LD_008_006_002_00_00_0_19990415