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