atovsin [ parameter=value ] [ inputfile ... ]
Parameters are year, atovs_types, calibrate, bright_temp.
atovsin creates TeraScan Advanced Microwave Sounding Unit (AMSU)-A, AMSU-B and High-Resolution Infrared Radiation Sounder (HIRS/3) sensor datasets. This suite of sensors makes up the Advanced Tiros Operational Vertical Sounder (ATOVS) system on the NOAA-KLM set of polar orbiting satellites. The data for these sensors is embedded within the High Resolution Picture Transmission (HRPT) telemetry. To retrieve AMSU and HIRS data, the hrptin function must first be used to extract the TIP/AIP data by selecting "tip" for the hrpt_types parameter (see EXAMPLES). This will produce a "raw" file of 512 byte TIP, spare and AIP records. Typically, this file will have a ".tip" extension. The AMSU data is contained within the AIP records and the HIRS data is contained within the TIP records. atovsin reads these "tip" files and optionally outputs AMSU-A, AMSU-B and/or HIRS datasets in an earth-locatable image format.
The AMSU-A sensor is a microwave radiometer used primarily for measuring global atmospheric temperature profiles and for providing information on atmospheric water in all of its forms (with the exception of small ice particles) from the NOAA KLM spacecraft. AMSU-A is a cross-track, line-scanned instrument designed to measure scene radiances in fifteen discrete frequency channels which permit the calculation of the vertical temperature profile from about 3 millibars (45 km) to the Earth's surface. At each channel (i.e., frequency), the antenna beamwidth is a constant 3.3 degrees (at the half power point). Thirty contiguous scene resolution cells are sampled in a stepped-scan fashion every eight seconds, each scan covering 50 degrees on each side of the subsatellite path. These scan patterns and geometric resolution translate to a 50 km diameter cell at nadir and a 2,343 km swath width from the 833 km nominal orbital altitude. AMSU-A channels one and two are at 23.8 and 31.4 GHz, respectively; channels three through fourteen span a frequency range of 50.3 to 57.29 GHz; and channel fifteen is at 89.0 GHz. The names of these channels in the AMSU-A output files are channel_nn, where nn ranges between 01 and 15. More detailed information on the AMSU-A sensor can be found in Section 3.3 of the NOAA-KLM User's Guide (see REFERENCES).
AMSU-B is a five channel microwave radiometer. The purpose of the instrument is to receive and measure radiation from a number of different layers of the atmosphere in order to obtain global data on humidity profiles. It works in conjunction with the AMSU-A instruments to provide a twenty channel microwave radiometer. AMSU-B is a cross-track, line scanned instrument designed to measure scene radiances in five channels. At each channel frequency, the antenna beamwidth is a constant 1.1 degrees (at the half power point). Ninety contiguous scene resolution cells are sampled in a continuous fashion, each scan covering 50 degrees on each side of the subsatellite path. These scan patterns and geometric resolution translate to a 16.3 km diameter cell at nadir at a nominal altitude of 850 km. The first two channels are centered at 89 and 150 GHz, respectively, and the latter three channels centered around 183.31 GHz. The names of these channels in the AMSU-B output files are channel_nn, where nn ranges between 16 and 20. More detailed information on the AMSU-B sensor can be found in Section 3.4 of the NOAA-KLM User's Guide (see REFERENCES).
The S band transmitters on NOAA-15 have been shown to interfere with AMSU-B. The effect is largest on channels 17 and 19, but has been shown to be present in the other channels also. The errors affect the Earth views, the space views, and to a lesser extent the internal views. atovsin performs NOAA-15 AMSU-B correction using the bias correction tables and procedures provided by NOAA.
HIRS/3 is a discrete stepping, line-scan instrument designed to measure scene radiance in twenty spectral bands to permit the calculation of the vertical temperature profile from Earth's surface to about 40 km. Multispectral data from one visible channel (0.69 micrometers), seven shortwave channels (3.7 to 4.6 micrometers) and twelve longwave channels (6.5 to 15 micrometers) are obtained from a single telescope and a rotating filter wheel containing twenty individual filters. An elliptical scan mirror provides cross-track scanning of 56 increments (i.e. samples) of 1.8 degrees. The mirror steps rapidly (<35 msec), then holds at each position while the 20 filter segments are sampled. This action takes place each 100 msec. The instantaneous FOV for each channel is approximately 1.4 degrees in the visible and shortwave IR and 1.3 degrees in the longwave IR band which, from an altitude of 833 kilometers, encompasses an area of 20.3 kilometers and 18.9 kilometers in diameter, respectively, at nadir on the Earth. The channel wavelengths (in micrometers) are as follows:
1 14.95 11 7.33 2 14.71 12 6.52 3 14.49 13 4.57 4 14.22 14 4.52 5 13.97 15 4.47 6 13.64 16 4.45 7 13.35 17 4.13 8 11.11 18 4.00 9 9.71 19 3.76 10 12.47 20 0.690
The channels listed above are designated channel_nn in the HIRS/3 output dataset, where nn ranges between 01 and 20.
The calibration of HIRS/3 follows the procedure described in Section 7.2 of the NOAA KLM User's Guide (see REFERENCES). The HIRS/3 instrument measures all radiation falling on the detector. Most optical components experience temperature changes very slowly with respect to the times between calibration cycles (256 seconds). However, the baffle (identified as the secondary mirror) is a blackened light material which is subject to short-term temperature changes from emission and absorption of radiation. The radiation sources include the internal blackbody (about 280 K), space (2.73 K), and the variable earth views (about 200-275 K plus reflected sunlight). To account for the contribution by the baffle, the space counts and blackbody temperature counts at each calibration cycle, and the interpolated (to the midpoint of the radiometric data) secondary mirror temperatures, are accumulated daily. The statiscal means of the calibration coefficients are evaluated at the end of a day, and then applied during the next day. The following are the steps required for HIRS/3 calibration:
Step 1. Run atovsin using the TIP files as input. This produces a file nxxhirs_calib.yyyyddd (where xx is the satellite number, yyyy is the year, and ddd is the julian date) that contains the HIRS calibration data needed for doing daily statistics.
Step 2. At the end of a day, run the script calstats using the nxxhirs_calib.yyyyddd file as input. This generates two files – nxxcalib_a1 and nxxcalib_b1 – to be used the next day.
Step 3. When atovsin is run the next day, it will look for the nxxcalib_a1 and nxxcalib_b1 files. If they are found, they will be processed for the HIRS calibration. If for any reason they are not found, atovsin will use the calibration data from the current pass to perform HIRS calibration.
The names of the sensor output datasets are automatically generated from the input file names by simply appending an extension on the end of the input filename. AMSU-A, AMSU-B and HIRS/3 dataset names have ".amsua", ".amsub" and ".hirs", respectively, appended to the input file name. If the input file name has a ".tip" extension (the default for hrptin), it is stripped off before the output extension is appended.
This example demonstrates the two step process required to produce AMSU and/or HIRS datasets. The first step involves using hrptin to produce a "tip" file. The second step involves using this "tip" file as input to atovsin.
% hrptin output file(s) : char(255) ? [.] hrpt_types : char( 17) ? [avhrr] tip on_pass_disk : char( 3) ? [yes] pass_number : int ( 2) ? [2] use_master : char( 3) ? [yes] n start_time : char( 15) ? [00:00:00] num_tip_lines : int ? [2000] pass partition 2: noaa-15 98/11/12 01:28:09.031 n15.98316.0128.tip: Creating ... n15.98316.0128.tip: 3775 records (TIP, Spare or AIP) written, 0 with no odd parity words. % atovsin n15.98316.0128.tip year : int ? [] 1998 atovs_types : char( 17) ? [amsua amsub hirs] calibrate : char( 3) ? [yes] bright_temp : char( 3) ? [yes] Processing n15.98316.0128.tip EOF reached after reading 3775 records. TIP Parity Results: good 5728 bad 507. AIP Parity Results: good 5742 bad 490. n15.98316.0128.amsub: Actual size is 203 lines by 90 samples n15.98316.0128.amsua: Actual size is 65 lines by 30 samples n15.98316.0128.hirs : Actual size is 82 lines by 56 samples
$SATDATA/satellite/sensor, orbdata, devtable
atovs, hrptin, amsu_a_ret, amsu_b_ret, datasets, etx, fixline, master.
The NOAA-KLM User's Guide can be found at: http://www2.ncdc.noaa.gov/docs/klm/index.htm
Last Update: $Date: 2002/02/09 02:04:02 $