CAMEX-3 NPOESS Aircraft Sounder Testbed- Microwave Temperature Sounder (NAST-MTS)
Table of Contents
Introduction
The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Aircraft Sounder Testbed- Microwave Temperature Sounder (NAST-MTS) is very much as the name suggests; an aircraft mounted Microwave Temperature Sounder. The instrument, built by Massachusetts Institute of Technology's Research Laboratory of Electonics (RLE), is about the size of a footlocker, and is mounted inside the forward section of one of the wing mounted 'superpods' of the NASA ER-2 aircraft, shown below.
NAST-MTS is a scanning radiometer which sweeps from side to side viewing a path that is sixty five degrees either side of nadir. MTS covers 16 microwave frequencies in the vicinity of 54 gigahertz and 118 gigahertz in each of its scans. This results in an image that is approximately 80 kilometers wide measured from the aircraft altitude (~20km). The radiometer 'sees' in the microwave portion of the elecromagnetic spectum. Images produced by the instrument represent the thermal radiation emitted by the environment at these microwave frequencies. Each microwave frequency responds differently to temperatures at different altitudes as well as to the different constituents such as water vapor, precipitation and ice. By combining the information gathered from MTS with information derived from the sensors in both the visible and infrared regions of the spectrum, the structure and composition of the atmosphere in the field of view as well as surface characteristics may be determined. Since microwave frequencies penetrate clouds much more readily than do infrared or visible, internal structure becomes apparent. By measuring the location, intensity and altitude of the strong ice signal, inferences can be made of the convective activity and intensity in the storm.
Distribution of liquid and frozen water as well as water vapor are important signals that can provide an insight into the dynamic mechanisms involved with hurricanes. By providing this information, NAST-MTS gives researchers a tool for understanding the life cycle of the tropical storm.
Data Documentation
The data is provided in a form readily usable with MatLab (see http://www.mathworks.com/products/matlab). Included with the data is a file which is a function call to be used with MatLab in order to read the binary and nav data.
read_camex.m
function [x, Tb, rtdf, t, nav, navt] = read_camex(datecode)
% quick and easy (i.e. slow) matlab reader for NAST-M Camex-3 files
%
0sage: [x, Tb, rtdf, t, nav, navt] = read_camex(datecode)
%
% datecode is ddMmmyy (ex: '02Sep98')
%
% function assumes the file is in your current working directory
%
% x: uncalibrated radiances
% Tb: calibrated radiances
% rtdf: rtd temperature measurements
% t: UTC timestamps for above (seconds since Jan. 1, 1970)
% nav: navigation records collected from ER-2
% navt: UTC timestamps for above (seconds since Jan. 1, 1970)
NUM_CHANS = 16; umber of channels
NUM_SPOTS = 25;
filename = ['CAMEX_NASTM_' datecode '.bin'];
nav_filename = ['CAMEX_NASTM_nav_' datecode '.bin'];
if exist(nav_filename)~= 2
fprintf('It appears that navigation data is not available...skipping.\n');
NAV = 0;
else
NAV = 1;
NUM_NAV_PARAMS = 48; umber of nav. items per record
end
if NAV
fprintf('Opening archive for . Input files are:\n\n\n', datecode, filename, nav_filename);
else
fprintf('Opening archive for . Input file is: \n', datecode, filename);
end
0pen radiometric stuff
fid = fopen(filename,'rb');
if (fid < 0)
error('Error opening file. Check to make sure it''s in the current directory')
end
NUM_SCANS = fread(fid,1,'integer*4')
NUM_RTDS = fread(fid,1,'integer*4')
0re-allocate matrices
x = zeros(NUM_CHANS,NUM_SPOTS,NUM_SCANS);
Tb = x;
rtdf = zeros(NUM_RTDS, NUM_SCANS);
t = zeros(1,NUM_SCANS);
% slow, terrible loops, but mnemonic
% read uncalibrated radiances
for i = 1:NUM_SCANS
for j = 1:NUM_SPOTS
for k = 1:NUM_CHANS
x(k,j,i) = fread(fid,1,'integer*2');
end
end
fprintf('Loaded record 0 of 0\r', i, NUM_SCANS);
end
fprintf('Finished loading uncalibrated radiances.\n');
% read calibrated radiances
for i = 1:NUM_SCANS
for j = 1:NUM_SPOTS
for k = 1:NUM_CHANS
Tb(k,j,i) = fread(fid,1,'float');
end
end
fprintf('Loaded record 0 of 0\r', i, NUM_SCANS);
end
fprintf('Finished loading calibrated radiances.\n');
% read rtds
for i = 1:NUM_SCANS
for j = 1:NUM_RTDS
rtdf(j,i) = fread(fid,1,'float');
end
fprintf('Loaded record 0 of 0\r', i, NUM_SCANS);
end
fprintf('Finished loading RTD readings. \n');
% read time
for i = 1:NUM_SCANS
t(i) = fread(fid,1,'integer*8');
fprintf('Loaded record 0 of 0\r', i, NUM_SCANS);
end
fprintf('Finished loading timestamps. \n');
fclose(fid);
if NAV % read nav
fid = fopen(nav_filename,'rb');
if (fid < 0)
error('Error opening nav file. Check to make sure it''s in the current directory')
end
NUM_NAV_RECORDS = fread(fid,1,'integer*4');
nav = zeros(NUM_NAV_PARAMS, NUM_NAV_RECORDS);
navt = zeros(1, NUM_NAV_RECORDS);
for i = 1:NUM_NAV_RECORDS
for j = 1:NUM_NAV_PARAMS
nav(j,i) = fread(fid,1,'float');
end
fprintf('Loaded record 0 of 0\r', i, NUM_NAV_RECORDS);
end
for i = 1:NUM_NAV_RECORDS
navt(i) = fread(fid,1,'integer*8');
end
fclose(fid);
end
fprintf('Finished loading. \n');
File Content and File Naming Convention
The file named README_NASTM_CAMEX is also included with the data. It describes the data format and naming conventions.
README_NASTM_CAMEX
NOTE: The binary files were written with a LITTLE-ENDIAN machine
Two files are written:
CAMEX_NASTM_ddmmm98.bin
The first number written, NUM_SCANS (32-bit integer), gives the number
of records contained in the file. The second value, NUM_RTDS
(32-bit integer), gives the number of housekeeping temperatures
recorded during the flight. The remainder of the file is organized
as follows:
1) uncalibrated radiance counts (16 x 25 x NUM_SCANS)
(16-bit signed integers)
The first dimension is channel frequency (in GHz):
1 50.30 +/- .090
2 51.76 +/- .200
3 52.80 +/- .200
4 53.75 +/- .120
5 54.40 +/- .200
6 54.94 +/- .200
7 55.50 +/- .165
8 56.02 +/- .135
9 118.75 +/- 3.50 +/- .500
10 118.75 +/- 2.55 +/- .250
11 118.75 +/- 2.05 +/- .250
12 118.75 +/- 1.60 +/- .200
13 118.75 +/- 1.20 +/- .200
14 118.75 +/- .800 +/- .200
15 118.75 +/- .450 +/- .150
16 118.75 +/- .235 +/- .065
The second dimension is spot number:
1 zenith (0 degrees)
2 zenith
3 heated calibration
4 heated calibration
5 - 23 nadir (-64.8 to 64.8 in steps of 7.2 degrees)
24 ambient calibration
25 ambient calibration
The third dimension is scan number.
2) calibrated brightness temperatures (32-bit floats)
(same organization as above)
3) housekeeping temperatures (NUM_RTDS x NUM_SCANS)
(num(32-bit floats)
Various RTD measurements of instrument thermometric
temperature, including calibration target are recorded during
flight. The order was changed a couple of times during the
deployment. The nominal ordering is:
1: 118 Radiometer: mixer
2: 118 Radiometer: heatsink
3: 118 Radiometer: LO
4: 118 Radiometer: IF
5: 54 Radiometer: IF
6: 54 Radiometer: LO
7: 54 Radiometer: mixer
8: 54 Radiometer: RF
9: Hot Load: corner/top
10: Hot Load: corner/bucket
11: Hot Load: side/aluminum
12: Hot Load: bottom/aluminum (control RTD)
13: Hot Load: middle-side/bucket
14: Hot Load: side/bucket
15: Hot Load: side/aluminum
16: CPU heatsink
17: Flight PC box interior
18: IF plate
19: Video processor (wall of rack)
20: power supply rack
21: camera mount
22: stepper motor
23: Cold Load: side/bucket
24: Cold Load: side/tip
25: Cold Load: side/tip
26: Cold Load: corner/bucket
27: Cold Load: corner/bucket
4) timestamps (1 x NUM_SCANS) (64-bit signed integers)
"POSIX-time" (seconds since Jan. 1, 1970)
When navigation data is available from the ER-2, a second file is written:
CAMEX_NASTM_nav_ddmmm98.bin.
The first number written, NUM_NAV_RECORDS (32-bit integer), gives
the number of records contained in the file. The remainder of the
file contains:
1) The 48 parameters given in the ER-2 Investigators Handbook
(II-4-1) are stored. All values are stored as 32-bit
floats. (48 x NUM_NAV_RECORDS)
2) timestamps (1 x NUM_SCANS) (64-bit signed integers)
"POSIX-time" (seconds since Jan. 1, 1970)
A NOTE ON THE TIMESTAMPS
^^^^^^^^^^^^^^^^^^^^^^^^
The POSIX-time values are calculated from UTC-time which is received
from the ER-2. The calculation is as follows:
POSIX-time = tm_sec + tm_min*60 + tm_hour*3600 + tm_yday*86400 +
(tm_year-70)*31536000 + ((tm_year-69)/4)*86400
where UTC time is broken into tm_year:tm_day:tm_hour:tm_min:tm_sec
The UTC timestamps are stored as part of the navigation record, so conversions
to either timestamp type are possible.
Please address questions and comments to Bill Blackwell (wjb@mit.edu)
Contact Information
To order these data or for further information, please contact:
Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: support-ghrc@earthdata.nasa.gov
Web: http://ghrc.nsstc.nasa.gov/
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