GAMMA DIFF/GEO: Reference Manual

atm_mod

ANSI-C program: atm_mod.c

NAME
atm_mod - Evaluate linear regression of unwrapped phase with respect to height and calculate a model of the atmospheric phase

SYNOPSIS
atm_mod <diff_unw> <hgt> <DIFF_par> <model> [dr] [daz] [overlay]

<diff_unw>	unwrapped differential interferogram including atmospheric phase signal (float)
<hgt>	(input) height coregistered to the interferogram
<DIFF_par>	(input) differential interferogram parameters
<model>	(output) modeled phase values from the regression of phase with respect to height (float)
[dr]	range sample increment (enter - for default: 32)
[daz]	azimuth sample increment (enter - for default: 32)
[overlay]	(input) SUN raster/BMP format overlay mask, 0 pixels are excluded ( -: no overlay)

EXAMPLE
atm_mod 19960421_19960422.adf.unw lan_dem.rdc 19960421_19960422.diff_par 1996421_19960422.atm_model 4 4

determines the linear regression coefficients of the residual phase with respect to height in the unwrapped interferogram19960421_19960422.adf.unw using the height data in lan_dem.rdc and generates the phase model of the height dependent atmospheric phase delay.

DESCRIPTION
This program is used to determine the height dependence of the unwrapped atmosphereric phase. This means that any topographic related phase due to the interferometric baseline must first be removed. Depending on atmospheric conditions there is an altitude dependence of the path delay with respect to altitude caused by changes in the atmospheric water vapor and preassure profiles between the acquisitions of the interferometric image pair. atm_mod estimates the parameters of a linear model of the residual phase with respect to the altitude values in the input height stack phgt. The model consists of a phase constant a0 in radians and phase slope a1 in unitis of radians per meter.

It is important that only phase due to atmosphere is present in the differential interferogram phase. For this reason the raster image overlay should be applied used to exclude any moving points from consideration in the regression. The overlay image must be an 8 bit raster image, all points in the image with RGB value 000 are excluded from the regression. The overlay should have the exact number of rows and columns as the unwrapped phase file.

The output phase model has the height dependent unwrapped phase as determined from the regression: model [x,y] = a0 + a1*hgt[x,y]. The program sub_phase can then be used to remove the modelled phase from all the points in the stack. The phase model is calculated for all points where valid height values are available not just those in the overlay. Valid heights are defined as non-zero values in the set of point heights.

SEE ALSO
sub_phase