t2edr [ parameter=value ... ] [ inputfile ... ]
Parameters are: af_elevation, method, dew_point, rh_calc, regress_150, maxrh, minrh, maxsh, minsh, maxwv, minwv.
t2edr derives atmospheric humidity, dew point, and water vapor profiles from SSM/T2 brightness temperature datasets. t2edr implements the Air Force Global Weather Center (AFGWC) D-matrix algorithm to compute relative and specific humidity at standard pressure levels, along with the water vapor mass in between these levels. In addition to the five SSM/T2 brightness temperatures, the calculation uses the first four SSM/T1 brightness temperatures, the 1000, 850 and 750 millibar derived heights (t1edr), and takes into account the elevation and viewing angles of the sensor footprints. Dew point values are calculated as a diagnostic from the derived temperature profiles (t1edr) and either the specific or relative humidity profiles (see rh_calc below).
The named input files must be SSM/T2 TeraScan datasets output from the DMSP ingest functions rtdin(1) or rdsin(1). Thus, the input filenames must have the suffix ".t2_s", meaning SSM/T2 sensor dataset. As indicated above, t2edr also requires the corresponding SSM/T1 sensor and environmental datasets. These two datasets should reside in the same directory as the SSM/T2 sensor dataset and have filename suffixes ".t1_s" and ".t1_e", respectively. Except for these suffixes, their filenames should have the same form as the SSM/T2 input filename. Output filenames are generated to have the same form as the input filenames, except with the suffix ".t2_e", meaning SSM/T2 environmental dataset.
The output datasets contain essentially three dimensions: lines, samples and pressure levels. The number of lines depends on the length of the satellite pass being processed. The number of samples is fixed by the SSM/T2 to be 28. The number of pressure levels is 6. These denote the following fixed-pressure surfaces: 1000, 850, 700, 500, 400 and 300 millibars. These pressure level values are stored in the one-dimensional output variable press_levels.
The relative humidity, specific humidity, dew point temperature, dew point depression, along with the water vapor mass, are each stored as three-dimensional variables. The vertical dimension of the humidity and dew point profiles is 6 levels, while for the water vapor variable, it is 7 layers. The first layer represents the layer between the surface and 1000 mb, the second represents the layer between 1000 and 850 mb, and so on. A one-dimensional variable called press_midlevels contains linearly interpolated millibar values signifying the pressure at these layers, hence 350 mb for the layer between 300 and 400 mb, and 150 mb for the layer above 300 mb. Note: since information about the surface pressure is not known, the first layer is (somewhat arbitrarily) assigned the value 1025 mb.
The output dataset also contains the following two-dimensional (lines and samples) variables: geography type, quality flag, atmospheric type and elevation.
The geography types and their meanings are as follows:
Geography Types --------------- 1 : Ocean 2 : Land 3 : Ice 4 : Coast
The values of the quality flag and their meanings are as follows:
Quality Flag ------------------------------------------------ 0 : "good" retrieval 1 : retrieval that may be contaminated by clouds (liquid water > 0.15 kg/m2) 2 : missing retrieval due to missing SSM/T2 data 3 : missing retrieval due to missing SSM/T1 data 4 : bad retrieval due to an algorithm error Note: When the height of a pressure level lies below the elevation, the retrievals for that level are set to bad value regardless of the value of the Quality Flag.
The atmospheric types and their meanings are as follows:
Atmospheric Types ----------------------------- 01 - 05 : Ocean 06 - 08 : Land at 0000 meters 09 - 11 : Land at 1500 meters 12 - 14 : Land at 3000 meters 15 - 17 : Land at 4500 meters 18 - 20 : Land at 6200 meters 21 - 22 : Sea Ice 23 - 25 : Coast
Output datasets contain the processing history (see audit) of the SSM/T1 and SSM/T2 sensor datasets and the SSM/T1 environmental datasets. Output datasets can be examined using the functions xvu, printvar, contents, burst, stats, etc.
If af_elevation=yes, then the AFGWC elevation dataset is used for the retrieval scheme. This dataset is stored in the form of an "1/8 meso-scale (mesh) grid". Each hemisphere contains 512 x 512 points, with the pole at the center of the grid; therefore the resolution is approximately 1/3 degree. The elevation at each SSM/T2 footprint is assigned the elevation of the grid point that has its center closest to the center of the sensor footprint. If af_elevation=no, then the elevation dataset is the etop05 topography dataset. This dataset is provided at 5 minute intervals over the globe; therefore, the grid contains (12 x 360) x (12 x 180) points (i.e., 1/12 degree resolution). See parameter method to specify options for assigning the elevation value to SSM/T2 footprints when using the etop05 dataset.
Valid responses are [yes or no]. The default is yes.
If af_elevation=no, then the value of method determines the manner in which the etop05 elevation values are assigned to individual SSM/T2 footprints. Since the size of the SSM/T2 footprint near nadir is about 175 km and the etop05 elevation dataset has a resolution of about 9 km (or less), several options are provided for specifying the elevations.
Use the elevation value closest to the sensor footprint center.
Use the mean of the elevation values within an area approximately the size of a SSM/T2 footprint at nadir.
Use the median of the elevation values within an area approximately the size of a SSM/T2 footprint at nadir.
Use the maximum elevation value within an area approximately the size of a SSM/T2 footprint at nadir.
Use the minimum elevation value within an area approximately the size of a SSM/T2 nadir footprint.
Note: processing time is least for method=center.
Valid responses are [center, mean, median, max, min]. The default is mean.
Specifies whether dew point temperature and dew point depression profiles are to be calculated.
The default value is [no].
Since the specific and relative humidities are derived independently, they are not necessarily consistent with the derived (SSM/T1) temperature values for the given pressure surface. When rh_calc=yes, the the dew point temperature and dew point depression are calculated from the derived relative humidity. When rh_calc=no, the dew point values are calculated from a relative humidity computed from the derived specific humidity, temperature, and pressure level value.
The default value is [yes].
OPTIONAL. Specifies whether the 150 Ghz channel is to be computed via linear regression for passes acquired after June, 1993. See NOTES.
The default value is [yes]. This parameter can only be set by an explicit specification on the command line.
OPTIONAL. Specifies the maximum "good" value for relative humidity retrievals (in percent), values exceeding this are set to bad value.
The default value is [95]. This parameter can only be set by an explicit specification on the command line.
OPTIONAL. Specifies the minimum "good" value for relative humidity retrievals (in percent), values below this are set to bad value.
The default value is [0]. This parameter can only be set by an explicit specification on the command line.
OPTIONAL. Specifies the maximum "good" value for specific humidity retrievals (in gm/kg), values exceeding this are set to bad value.
The default value is [95]. This parameter can only be set by an explicit specification on the command line.
OPTIONAL. Specifies the minimum "good" value for specific humidity retrievals (in gm/gk), values below this are set to bad value.
The default value is [0]. This parameter can only be set by an explicit specification on the command line.
OPTIONAL. Specifies the maximum "good" value for water vapor retrievals (in kg/m2), values exceeding this are set to bad value.
The default value is [95]. This parameter can only be set by an explicit specification on the command line.
OPTIONAL. Specifies the minimum "good" value for water vapor retrievals (in kg/m2), values below this are set to bad value.
The default value is [0]. This parameter can only be set by an explicit specification on the command line.
This example shows how to execute t2edr on an SSM/T2 dataset created in the manner shown in the EXAMPLES section of rtdin. This example assumes that t1edr has already been executed as shown in the EXAMPLES section of that manual page.
% t2edr
input file(s) : char(255) ? f11.92351.1415_t2_s
af_elevation : char( 3) ? [yes]
dew_point : char( 3) ? [no] y
rh_calc : char( 3) ? [yes]
Processing f11.92351.1415_t2_s
SSM/T2 data starts at 14:15:19.371 GMT on 92/12/16.
TDF data set f11.92351.1415_t2_e created.
% contents f11.92351.1415_t2_e
printout : char( 3) ? [no]
Contents of File: f11.92351.1415_t2_e Page 1
Dimension Size Coord Scale Offset
mt2line 98 y 1 0
mt2samp 28 x 1 0
standard_levels 6 ? 1 0
standard_layers 7 ? 1 0
Attribute Type Units Value
projection long std_projection sensor_scan
et_affine double 1 0 0 1 0 0
satellite string12 f-11
sensor long std_sensor ssmt2
pass_date long std_date 92/12/16
start_time double std_time 14:15:19.371
time_adjust double std_time 00:00:00
attitude double radians 0 0 0
sensor_tilt double radians 0
scan_samples long 28
scan_rates double 0.125 5.303 -0.267751
sensorient double radians 0 0.785398 0 0.706858
-0.706858
orb_elem_date long std_date 92/12/16
orb_elements double 0.237152 0.829383 4e-05
0.0012575 0.697166 0.72245
0.274848
history byte
Variable Type Units
press_levels float millibars
press_midlevels float millibars
rel_humidity float percent
spec_humidity float gm/kg
dew_point short celsius
dew_point_dep short celsius
water_vapor float kg/m3
geography_type byte
quality_flag byte
atmos_type byte
elevation short meters
Variable Dimension Size
press_levels standard_levels 6
press_midlevels standard_layers 7
rel_humidity mt2line 98
rel_humidity mt2samp 28
rel_humidity standard_levels 6
spec_humidity mt2line 98
spec_humidity mt2samp 28
spec_humidity standard_levels 6
dew_point mt2line 98
dew_point mt2samp 28
dew_point standard_levels 6
dew_point_dep mt2line 98
dew_point_dep mt2samp 28
dew_point_dep standard_levels 6
water_vapor mt2line 98
water_vapor mt2samp 28
water_vapor standard_layers 7
geography_type mt2line 98
geography_type mt2samp 28
quality_flag mt2line 98
quality_flag mt2samp 28
atmos_type mt2line 98
atmos_type mt2samp 28
elevation mt2line 98
elevation mt2samp 28
Variable BadValue ValidMin ValidMax Scale Offset
press_levels -3.4028e+38 -3.4028e+38 3.4028e+38 1 0
press_midlevels -3.4028e+38 -3.4028e+38 3.4028e+38 1 0
rel_humidity -10000 -32768 32767 0.01 0
spec_humidity -10000 -32768 32767 0.01 0
dew_point -10000 -32768 32767 0.01 0
dew_point_dep -10000 -32768 32767 0.01 0
water_vapor -10000 -32768 32767 0.01 0
geography_type 255 0 255 1 0
quality_flag 255 0 255 1 0
atmos_type 255 0 255 1 0
elevation -32768 -32768 32767 1 0
$TSCANROOT/refdata/ssp/af_geog.tdf $TSCANROOT/refdata/ssp/af_elev.tdf $TSCANROOT/refdata/bathy/etop05 $TSCANROOT/refdata/satel/f-*/t2dmatrix.tdf $TSCANROOT/refdata/satel/f-*/t2alphabeta.tdf
dmsp, ols, ssmt, geoph, rtdin, rdsin, t1edr, miedr, datasets.
In June, 1993 the 150 Ghz channel went out of specification. For passes acquired after this date, the 150 Ghz channel is computed via multiple linear regression from the other four SSMT/2 channels and the first four SSMT/1 channels. The regression coefficients are supplied by the Air Force Global Weather Center.
References:
System Summary Report for the SSM/T-2 Water Vapor Profiling Sensor Hardware Segment. Aerojet, Report 9538, CDRL 035A2, 18 June 1980.
Last Update: $Date: 1998/05/29 20:52:54 $