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Washita '92 AIRSAR
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Washita '92 AIRSAR

AIRSAR is a side-looking imaging radar system which was flown on the NASA DC-8 aircraft in Washita'92.

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Data Sets: The data sets included here represent only a portion of the data collected. The primary criteria in selecting these was the availability of a time series and data quality. Two basic data sets are available; the NASA Goddard Space Flight Center set prepared by Ann Hsu and Peggy O'Neill (GSFC) and another prepared by Pascale Dubois of NASA Jet Propulsion Lab (JPL). These have different characteristics and will be treated separately.

GSFC DATA SET

Two sites were selected; a region near AG002 and another near MS003. Only L and C band data are included due to uncertainties in the P band calibration.

Data Values: The original full polarization data are stored in a compressed mode known as the Stokes matrix. Each pixel is stored as 10 byte data. To facilitate users not familiar with the format or sotware, the original data were decompressed and processed into single polarization decibel data scaled to one byte (binary). Each file represents a single site, date, band and polarization. Data are in scaled decibels (DN). The scaling varies with band and polarization as follows;

Actual dB (C HH) = (DN/(255/25)) - 25

Actual dB (C VV) = (DN/(255/25)) - 25

Actual dB (C HV) = (DN/(255/30)) - 35

Actual dB (L HH) = (DN/(255/35)) - 35

Actual dB (L VV) = (DN/(255/35)) - 35

Actual dB (L HV) = (DN/(255/35)) - 45

Note that computations involving spatial averaging, etc. must be done using power determined as follows

Power = (10^(dB/10))

Scene Geometry: The images provided are in slant range. Slant range is the radial distance of the image object from the radar. Ground range is a measure of the distance of the object from a point directly below the aircraft.

The algorithm used to convert from slant to ground range is from the PCI radar package. The name of the PCI program is SRTOGR. The algorithm used by SRTOGR is derived from the FLTIMA program, which is part of LDIAS (Landsat Digital Image Analysis System) developed by CCRS (Canada Centre for Remote Sensing) in Ottawa, Canada. The equations were derived with the help of Dr. Bert Guindon of CCRS who wrote the original FLTIMA program.

The algorithm is output driven. For each output pixel location in the output window on the master (output) file, the corresponding input pixel location on the uncorrected (input) file is determined. The pixel value at the input pixel location is copied to the output pixel location.

The following values are constant for each output location:

HEIGHT = height above ground
INPXSZ(1) = input SAR image pixel spacing in range direction
INPXSZ(2) = output SAR image pixel spacing (normally one can use the input SAR image pixel spacing in azimuth direction)
S0 = slant range to first pixel
G0 = ground range to first pixel

If S0 <= HEIGHT, then G0 = 0

Compute slant range pixel N given ground range pixel M:

N = (SQRT((G0 + M*INPXSZ(2))**2+HEIGHT**2) - S0) / INPXSZ(1)

Compute ground range pixel M given slant range pixel N:

M = (SQRT((S0 + N*INPXSZ(1))**2-HEIGHT**2) - G0) / INPXSZ(2)

All images have dimension of 1024 samples and 1279 lines. Parameters required for the conversion are listed below:

GSFC AIRSAR SLANT RANGE TO GROUND RANGE PARAMETERS
Date Scene Range
Spacing
(m)		 Azimuth
Spacing
(m)		 Flight
Height
(m)		 Slant Range to First Pixel
(m)		 Incidence Angle (Near)
(Deg.)
6/10/92 CM3902 6.6621 12.1532 7900.42 8364.21 19.1696
6/13/92 CM3359 6.6621 12.2056 7936.99 8364.21 18.3914
6/14/92 CM3875 6.6621 12.1365 7938.52 8364.21 18.3582
6/16/92 CM3883 6.6621 12.0848 8071.1 8364.21 15.213
6/18/92 CM3360 6.6621 12.0463 8084.21 8364.21 14.867
6/10/92 CM3849 6.6621 12.1365 7840.07 8364.21 20.3912
6/11/92 CM3931 6.6621 12.1427 7914.13 8364.21 18.8815
6/12/92 CM4000 6.6621 12.1486 7905.29 8364.21 19.0678
6/14/92 CM4054 6.6621 12.1264 7865.97 8364.21 19.8758
6/16/92 CM4017 6.6621 12.1582 8002.22 8364.21 16.9181
6/17/92 CM3954 6.6621 12.1272 7981.19 8364.21 17.4063
6/18/92 CM3665 6.6621 12.1229 7991.55 8364.21 17.1675

The images will appear upside down due to the aircraft flight direction. For geometric correction and scaling, the following georegistration information is provided for each image.

GSFC AIRSAR DATA GEOREGISTRATION INFORMATION
Site Date Scene Corner UTM
Easting
(m)		 UTM
Northing
(m)		 Longitude(W) Latitude(N)
Deg. Min. Sec. Deg. Min. Sec.
AG0002 6/10/92 CM3902 Upper Left 606032 3862022 97 50 22.33 34 53 48.68
AG0002 6/10/92 CM3902 Upper Right 595372 3868542 97 57 19.59 34 57 24.12
AG0002 6/10/92 CM3902 Lower Left 611482 3873532 97 46 42.1 35 0 0.15
AG0002 6/10/92 CM3902 Lower Right 601312 3879622 97 53 20.56 35 3 21.67
AG0002 6/13/92 CM3359 Upper Left 606372 3862182 97 50 8.86 34 53 53.75
AG0002 6/13/92 CM3359 Upper Right 595192 3867852 97 57 26.97 34 57 1.79
AG0002 6/13/92 CM3359 Lower Left 611502 3872722 97 46 41.7 34 59 33.86
AG0002 6/13/92 CM3359 Lower Right 600902 3878512 97 53 36.44 35 2 45.79
AG0002 6/14/92 CM3875 Upper Left 607852 3861562 97 49 10.85 34 53 33.06
AG0002 6/14/92 CM3875 Upper Right 595672 3867012 97 57 8.39 34 56 34.36
AG0002 6/14/92 CM3875 Lower Left 612512 3872522 97 46 1.97 34 59 26.96
AG0002 6/14/92 CM3875 Lower Right 601912 3877442 97 52 57.84 35 2 10.7
AG0002 6/16/92 CM3883 Upper Left 608062 3861192 97 49 2.75 34 53 20.97
AG0002 6/16/92 CM3883 Upper Right 598022 3866582 97 55 35.94 34 56 19.59
AG0002 6/16/92 CM3883 Lower Left 614472 3871802 97 44 45.03 34 59 2.8
AG0002 6/16/92 CM3883 Lower Right 603222 3876772 97 52 6.47 35 1 46.85
AG0002 6/18/92 CM3360 Upper Left 609222 3860982 97 48 17.15 34 53 13.71
AG0002 6/18/92 CM3360 Upper Right 597772 3866692 97 55 45.75 34 56 23.25
AG0002 6/18/92 CM3360 Lower Left 614302 3871652 97 44 51.81 34 58 58
AG0002 6/18/92 CM3360 Lower Right 603622 3877072 97 51 50.53 35 1 58.06
MS0003 6/10/92 CM3849 Upper Left 588282 3848622 98 2 6.66 34 46 39.84
MS0003 6/10/92 CM3849 Upper Right 577182 3854082 98 9 21.52 34 49 40.32
MS0003 6/10/92 CM3849 Lower Left 593262 3859242 97 58 46.51 34 52 22.96
MS0003 6/10/92 CM3849 Lower Right 582982 3864172 98 5 29.62 34 55 6.2
MS0003 6/11/92 CM3931 Upper Left 588472 3849092 98 1 59.01 34 46 55.03
MS0003 6/11/92 CM3931 Upper Right 577342 3853382 98 9 15.46 34 49 17.55
MS0003 6/11/92 CM3931 Lower Left 592522 3858062 97 59 16.12 34 51 44.9
MS0003 6/11/92 CM3931 Lower Right 582872 3864552 98 5 33.81 34 55 18.57
MS0003 6/12/92 CM4000 Upper Left 585592 3845142 98 3 53.76 34 44 47.7
MS0003 6/12/92 CM4000 Upper Right 574892 3850932 98 10 52.68 34 47 58.68
MS0003 6/12/92 CM4000 Lower Left 591122 3855162 98 0 12.39 34 50 11.22
MS0003 6/12/92 CM4000 Lower Right 581222 3861462 98 6 39.92 34 53 38.74
MS0003 6/14/92 CM4054 Upper Left 585402 3845282 98 4 1.18 34 44 52.3
MS0003 6/14/92 CM4054 Upper Right 574262 3851112 98 11 17.41 34 48 4.69
MS0003 6/14/92 CM4054 Lower Left 590782 3855482 98 0 25.64 34 50 21.72
MS0003 6/14/92 CM4054 Lower Right 580672 3861482 98 7 1.58 34 53 39.55
MS0003 6/16/92 CM4017 Upper Left 585022 3845722 98 4 15.96 34 45 6.7
MS0003 6/16/92 CM4017 Upper Right 573632 3850832 98 11 42.29 34 47 55.77
MS0003 6/16/92 CM4017 Lower Left 590392 3855692 98 0 40.92 34 50 28.66
MS0003 6/16/92 CM4017 Lower Right 579662 3861912 98 7 41.22 34 53 53.8
MS0003 6/17/92 CM3954 Upper Left 585102 3845552 98 4 12.88 34 45 1.16
MS0003 6/17/92 CM3954 Upper Right 574192 3850962 98 11 20.22 34 47 59.84
MS0003 6/17/92 CM3954 Lower Left 589972 3855392 98 0 57.57 34 50 19.06
MS0003 6/17/92 CM3954 Lower Right 580032 3862172 98 7 26.56 34 54 2.13
MS0003 6/18/92 CM3665 Upper Left 583682 3846462 98 6 9.75 34 45 31.58
MS0003 6/18/92 CM3665 Upper Right 572942 3851352 98 12 9.28 34 48 12.82
MS0003 6/18/92 CM3665 Lower Left 589222 3856272 98 1 26.76 34 50 47.86
MS0003 6/18/92 CM3665 Lower Right 578432 3863162 98 8 29.26 34 54 34.72

Data Files: Data are available via FTP - please email Rob Parry for access. File names and descriptions are presented in the following table.

GSFC AIRSAR DATA FILES
SITE SCENE ID DATE BAND POL FILE
AG002 CM3902 06/10/92 L HH ag002610lhh.byt
AG002 CM3902 06/10/92 L HV ag002610lhv.byt
AG002 CM3902 06/10/92 L VV ag002610lvv.byt
AG002 CM3902 06/10/92 C HH ag002610chh.byt
AG002 CM3902 06/10/92 C HV ag002610chv.byt
AG002 CM3902 06/10/92 C VV ag002610cvv.byt
AG002 CM3359 06/13/93 L HH ag002613lhh.byt
AG002 CM3359 06/13/93 L HV ag002613lhv.byt
AG002 CM3359 06/13/93 L VV ag002613lvv.byt
AG002 CM3359 06/13/93 C HH ag002613chh.byt
AG002 CM3359 06/13/93 C HV ag002613chv.byt
AG002 CM3359 06/13/93 C VV ag002613cvv.byt
AG002 CM3875 06/14/92 L HH ag002614lhh.byt
AG002 CM3875 06/14/92 L HV ag002614lhv.byt
AG002 CM3875 06/14/92 L VV ag002614lvv.byt
AG002 CM3875 06/14/92 C HH ag002614chh.byt
AG002 CM3875 06/14/92 C HV ag002614chv.byt
AG002 CM3875 06/14/92 C VV ag002614cvv.byt
AG002 CM3883 06/16/92 L HH ag002616lhh.byt
AG002 CM3883 06/16/92 L HV ag002616lhv.byt
AG002 CM3883 06/16/92 L VV ag002616lvv.byt
AG002 CM3883 06/16/92 C HH ag002616chh.byt
AG002 CM3883 06/16/92 C HV ag002616chv.byt
AG002 CM3883 06/16/92 C VV ag002616cvv.byt
AG002 CM3360 06/18/92 L HH ag002618lhh.byt
AG002 CM3360 06/18/92 L HV ag002618lhv.byt
AG002 CM3360 06/18/92 L VV ag002618lvv.byt
AG002 CM3360 06/18/92 C HH ag002618chh.byt
AG002 CM3360 06/18/92 C HV ag002618chv.byt
AG002 CM3360 06/18/92 C VV ag002618cvv.byt
MS003 CM3849 06/10/92 L HH ms003610lhh.byt
MS003 CM3849 06/10/92 L HV ms003610lhv.byt
MS003 CM3849 06/10/92 L VV ms003610lvv.byt
MS003 CM3849 06/10/92 C HH ms003610chh.byt
MS003 CM3849 06/10/92 C HV ms003610chv.byt
MS003 CM3849 06/10/92 C VV ms003610cvv.byt
MS003 CM3931 06/11/92 L HH ms003611lhh.byt
MS003 CM3931 06/11/92 L HV ms003611lhv.byt
MS003 CM3931 06/11/92 L VV ms003611lvv.byt
MS003 CM3931 06/11/92 C HH ms003611chh.byt
MS003 CM3931 06/11/92 C HV ms003611chv.byt
MS003 CM3931 06/11/92 C VV ms003611cvv.byt
MS003 CM4000 06/12/92 L HH ms003612lhh.byt
MS003 CM4000 06/12/92 L HV ms003612lhv.byt
MS003 CM4000 06/12/92 L VV ms003612lvv.byt
MS003 CM4000 06/12/92 C HH ms003612chh.byt
MS003 CM4000 06/12/92 C HV ms003612chv.byt
MS003 CM4000 06/12/92 C VV ms003612cvv.byt
MS003 CM4054 06/14/92 L HH ms003614lhh.byt
MS003 CM4054 06/14/92 L HV ms003614lhv.byt
MS003 CM4054 06/14/92 L VV ms003614lvv.byt
MS003 CM4054 06/14/92 C HH ms003614chh.byt
MS003 CM4054 06/14/92 C HV ms003614chv.byt
MS003 CM4054 06/14/92 C VV ms003614cvv.byt
MS003 CM4017 06/16/92 L HH ms003616lhh.byt
MS003 CM4017 06/16/92 L HV ms003616lhv.byt
MS003 CM4017 06/16/92 L VV ms003616lvv.byt
MS003 CM4017 06/16/92 C HH ms003616chh.byt
MS003 CM4017 06/16/92 C HV ms003616chv.byt
MS003 CM4017 06/16/92 C VV ms003616cvv.byt
MS003 CM3954 06/17/92 L HH ms003617lhh.byt
MS003 CM3954 06/17/92 L HV ms003617lhv.byt
MS003 CM3954 06/17/92 L VV ms003617lvv.byt
MS003 CM3954 06/17/92 C HH ms003617chh.byt
MS003 CM3954 06/17/92 C HV ms003617chv.byt
MS003 CM3954 06/17/92 C VV ms003617cvv.byt
MS003 CM3665 06/18/92 L HH ms003618lhh.byt
MS003 CM3665 06/18/92 L HV ms003618lhv.byt
MS003 CM3665 06/18/92 L VV ms003618lvv.byt
MS003 CM3665 06/18/92 C HH ms003618chh.byt
MS003 CM3665 06/18/92 C HV ms003618chv.byt
MS003 CM3665 06/18/92 C VV ms003618cvv.byt

Please email Rob Parry for access to the files listed above.

Quality Control Checks: The following quality control analysis was prepared by A. Hsu and P. O'Neill at NASA Goddard Space Flight Center.

AG002 - L band AIRSAR and L band truck radar measurements were available over the following bare soil field sites. There were no C band truck data in 1992. The AIRSAR scenes did not include an extended forest target that might be used as a calibration check, therefore, the quality of the C band data is unknown.

GSFC AIRSAR DATA QUALITY CONTROL-SITE AG002
SITE SCENE ID DATE BAND Backscattering Coefficient (dB)
AIRSARHH Truck HH AIRSAR VV Truck VV
AG012 CM3902 06/10/92 L -17.07 -16 -12.21 -12.7
AG012 CM3359 06/13/92 L -19.32 -19.1 -14.64 -16.7
AG012 CM3875 06/14/92 L -20.12 -19.15* -16.13 -17.15*
AG012 CM3883 06/16/92 L -20.15 -19.6 -17.73 -18.2
AG012 CM3360 06/18/92 L -20.83 -20.6 -19.63 -20.3
AG002 CM3902 06/10/92 L -17.88 -17.0 -12.4 -12.8
AG002 CM3359 06/13/92 L -20.31 -19.5 -16.11 -17.1
AG002 CM3875 06/14/92 L -20.85 -19.35* -16.13 -17.05*
AG002 CM3883 06/16/92 L -20.92 -20.2 -18.03 -18.1
AG002 CM3360 06/18/92 L -20.83 -20.7 -18.9 -19.2

* Average of 6/13/92 and 6/15/92

MS003 - Within the area of MS003 there was a deciduous forest target at an incidence angle of 50 degrees. By assuming that the backscattering coefficient is constant the calibration can be evaluated.

GSFC AIRSAR DATA QUALITY CONTROL-SITE MS003
SITE SCENE ID DATE Backscattering Coefficient (dB)
L HH L VV L HV C HH C VV C HV
MS003 CM3849 06/10/92 -6.69 -7.83 -12.98 -5.49 -7.43 -12.47
MS003 CM3931 06/11/92 -6.64 -8.01 -12.85 -5.49 -7.25 -12.28
MS003 CM4000 06/12/92 -6.95 -8.13 -13.14 -5.66 -7.14 -12.26
MS003 CM4054 06/14/92 -6.98 -8.11 -13.23 -4.82 -6.3 -11.45
MS003 CM4017 06/16/92 -6.84 -7.66 -12.85 -4.8 -5.72 -11.22
MS003 CM3954 06/17/92 -5.64 -6.73 -11.77 -3.35 -5.13 -10.19
MS003 CM3665 06/18/92 -6.74 -7.79 -12.76 -4.17 -5.44 -10.70

Except for 6/17/92, the L band data for a dense deciduous forest located at 50 degree incidence angle are stable day to day. Without the 6/17/92 data the backscattering coefficient varies as follows; 0.35 dB HH, 0.52 dB VV and 0.50 dB HV.

The C band vary a bit more than L band; 1.49 dB HH, 1.99 dB VV, and 1.77 dB HV (all without 6/17/92). The user must be aware that residual calibration errors remain in the data and are likely to be larger at C band than L band.

JPL LITTLE WASHITA WATERSHED GEOREFERENCED AIRSAR DATA SET

As part of a research project to evaluate soil moisture and backscatter relationships, Pascale Dubois of NASA JPL (no longer affiliated with JPL) assembled a data set for the analysis of AIRSAR data in a spatial context. Many other types of data were included. All are georeferenced. The georeferencing was based on using ground control points selected on a SPOT image and topo maps. The georeferenced SPOT image was used to georeference the AIRSAR data. The DEM, soils and vegetation data bases were independently georeferenced. The soils and vegetation codes are the same as those used in the ESTAR studies. Reference information for all of the images is;

Pixel resolution: 30m

Projection: UTM

Number of pixels: 1533

Number of lines: 1000

Upper left coordinate: 564000E 3875000N

Lower right coordinate: 610000E 3845000N

The AIRSAR data selected covered a large portion of the Little Washita Watershed on two days June 13 and June 18, 1992. On June 18 two lines of data are used. The data were resampled to the 30 m resolution and only L band data were processed. The binary data are scaled backscattering coefficient values. The backscattering coefficient in dB is computed as follows;

Actual dB (L HH) = (DN/(255/40)) - 40

Actual dB (L VV) = (DN/(255/40)) - 40

Actual dB (L HV) = (DN/(255/40)) - 48

The following files are available via FTP - please email Rob Parry for access.

JPL LITTLE WASHITA WATERSHED AIRSAR DATA SET FILES
Description File
SPOT Band 2 7/2/92 lwspot2.bin
SPOT Band 3 7/2/92 lwspot3.bin
SPOT Band 4 7/2/92 lwspot4.bin
Digital Elevation Model Data lwdem.bin
AIRSAR 6/13/92 L HH lw613lhh.bin
AIRSAR 6/13/92 L VV lw613lvv.bin
AIRSAR 6/13/92 L HV lw613lhv.bin
AIRSAR 6/18/92 L HH lw618lhh.bin
AIRSAR 6/18/92 L VV lw618lvv.bin
AIRSAR 6/18/92 L HV lw618lhv.bin
Soil Texture lwsoil.bin
Land Cover lwland.bin

Please email Rob Parry for access to the files listed above.