GENAWVC

Description

Generates an atmospheric water vapor content map. The computations use radiance values interpolated from an at-sensor radiance lookup table.

Parameters

Name	Type	Length	Value range
Input *	String	1 -
InputRLUT *	Integer	1 - 1
InputDEM: Input scene elevation channel	Raster port	0 - 1
InputAOD: Input Aerosol Optical Depth map channel	Raster port	0 - 1
InputSMR: Input surface meteorological range map channel	Raster port	0 - 1
Output: Output water vapor content channel *	Raster port	1 - 1
OutputLWT: Output leaf water thickness channel	Raster port	0 - 1
OutputSSE: Output SSE channel	Raster port	0 - 1
Radiometric Transformation Level	Integer	0 - 1	0 -
Nominal Aerosol Optical Depth	Float	0 - 1	0.0 -
Nominal Surface Meteorological Range	Float	0 - 1	0.0 -
Nominal Scene Elevation	Float	0 - 1	0.0 -
Wavelength Range Start	Float	0 - 1	400 - 2400 Default: 850
Wavelength Range End	Float	0 - 1	400 - 2400 Default: 1250
Initial Water Vapor Content Guess	Float	0 - 1	0.11 - 5.09 Default: 2.5
Maximum Number of Iterations	Integer	0 - 1	5 - 100 Default: 25
Adjacency Effect Window Dimension	Integer	0 - 1	0 - Default: 1
Report	String	0 - 192	See parameter description

* Required parameter

Parameter descriptions

Input

Specifies the input hyperpectral image channels.

InputRLUT

Specifies the PCIDSK file segment that contains the radiance lookup table.

InputDEM: Input scene elevation channel

Optionally specifies the input channel containing a DEM map of the scene for which the atmospheric water vapor content is to be extracted.

If this parameter is not specified, a nominal elevation, specified by NOMELEV, will be used over the entire scene. Only one channel may be specified.

InputAOD: Input Aerosol Optical Depth map channel

Optionally specifies the input channel containing an aerosol optical depth map of the scene for which the atmospheric water vapor content is to be extracted.

If this parameter is not specified, a nominal aerosol optical depth, specified by NOMAOD, will be used over the entire scene. Only one channel may be specified.

This parameter is used as an alternative to DBSMR (InputSMR) for evaluating a surface meteorological range map; specify either DBAOD or DBSMR.

InputSMR: Input surface meteorological range map channel

Optionally specifies the input channel containing a surface meteorological range map of the scene for which the atmospheric water vapor content is to be extracted.

If this parameter is not specified, a nominal surface meteorological range, specified by NOMSMR, will be used over the entire scene. Only one channel may be specified.

This parameter is used as an alternative to DBSMR (InputSMR) for evaluating a surface meteorological range map; specify either DBSMR or DBAOD.

Output: Output water vapor content channel

Specifies the output channel to receive the extracted atmospheric water vapor content map over the scene.

Exactly one channel must be specified. The output channel must exist prior to running GENAWVC.

OutputLWT: Output leaf water thickness channel

Specifies the output channel to receive the extracted leaf water absorption map over the scene.

If this parameter is not specified, the leaf water thickness map is discarded. The specified channel must exist prior to running GENAWVC.

OutputSSE: Output SSE channel

Optionally specifies the output channel to receive the Sum of Squared Errors map over the scene.

If this parameter is not specified, the error map is discarded. The specified channel must exist prior to running GENAWVC.

Radiometric Transformation Level

Specifies the radiometric transformations already associated with the data set that are to be applied to the stored pixel values before they are used in the water vapor extraction computations. By default, GENAWVC applies the full sequence of transformations.

If the data set metadata contains no radiometric transformation parameter values, this parameter has no effect.

Nominal Aerosol Optical Depth

Specifies a nominal aerosol optical depth to be used over the entire scene.

For example:

NOMAOD = 1.1725

specifies an aerosol optical depth of 1.1724 over the entire scene, equivalent to an approximately 5 km meteorological range.

This parameter is used as an alternative to NOMSMR (Nominal SMR) for evaluating a nominal surface meteorological range value. Specify either NOMAOD or NOMSMR.

If either DBAOD (input AOD) or DBSMR (Input SMR) is specified, this parameter is ignored.

Nominal Surface Meteorological Range

Specifies a nominal surface meteorological range value (in km) to be used over the entire scene.

If the input RLUT was created by leaving the surface meteorological range settings unspecified in the programs GENTP5 and GENRLUT, this parameter should also be left unspecified.

If DBSMR (InputSMR) is specified, this parameter is ignored.

Nominal Scene Elevation

Specifies a nominal elevation value (in meters, with respect to the WGS84 vertical datum) to be used for the entire scene.

Either NOMELEV or DBDEM (InputDEM) must be specified; if DBDEM is specified, this parameter is ignored.

Wavelength Range Start

Specifies the start of the wavelength range, in nanometers, to be used for the extraction of the atmospheric water vapor content map.

A wavelength range start e must be such that:

400nm < e < 2400nm

The default wavelength start value is 850nm.

Wavelength Range End

Specifies the end of the wavelength range, in nanometers, to be used for the extraction of the atmospheric water vapor content map.

A wavelength range end e must be such that:

400nm < e < 2400nm

The default wavelength end value is 1250nm.

Initial Water Vapor Content Guess

Specifies an initial atmospheric water vapor content guess, in g/cm^2, to be used as a starting value in the spectra fitting algorithm.

A water vapor content guess e must be such that:

0.11 <=   e <= 5.09

The default initial water vapor content guess value is 2.5 g/cm^2.

Maximum Number of Iterations

Specifies the maximum number of iterations to be performed by the non-linear spectra fitting algorithm.

A maximum number of iterations e must be such that:

5 <= e <= 100

The default maximum number of iterations is 25.

Adjacency Effect Window Dimension

Specifies the dimension of the neighborhood window to include in the computation of adjacency radiance effects due to heterogeneous terrain reflectance.

Report

Specifies where to direct the generated report.

Available options are:

• LOG: generates a report on the terminal (default)
• <modulename.RPT>: appends a report to the module's RPT file
• DISK: generates a report on file "IMPRPT.LST"

Details

GENAWVC is used to extract atmospheric water vapor and leaf water absorption maps from an image data set and a matching RLUT. It builds on the results of GENTP5 GENRLUT, and RESRLUT, and outputs data that can later be used in ATRLUT and GENCLUT.

GENAWVC employs an inversion algorithm for retrieval of atmospheric water vapor content and leaf water thickness. The inversion algorithm operates on the spectrum of each spatial element and generates an atmospheric water vapor map over the entire scene. A non-linear least-squares fitting approach, coupled with a radiance lookup table generated by GENTP5 and GENRLUT, is used to minimize the error between the target spectrum within the start/end wavelength range specified and a modeled radiance spectrum. For reliable results, the range must cover the water absorption spectrum features.

GENAWVC will perform automatic resampling of the input at-sensor radiance lookup table (RLUT) if the wavelength dimension sampling does not match the data set band center wavelengths. Alternatively, the user may use RESRLUT to resample the RLUT to match the response profile of the data set before running GENAWVC; this will result in a considerable reduction of the GENAWVC execution time.

On completion, GENAWVC outputs the retrieved atmospheric water vapor content map, the equivalent leaf water thickness map, and the sum of squared errors (SSE) map to the user-specified output channels. If enabled, the generated report lists all image pixels for which the non-linear least-squares fitting technique failed and the reason for that failure. For all pixel locations for which the standard non-linear fitting method failed, an alternative slower but more robust method will be used instead (namely, the Downhill Simplex Method).

Acknowledgements

PCI Geomatics received financial support from the Canadian Space Agency/L'Agence Spatiale Canadienne through the Earth Observation Application Development Program (EOADP) for the development of this software, under contract 9F028-0-4914/09.

References

K. Staenz, Williams, D.J., 1997. Retrieval of Surface Reflectance from Hyperspectral data Using a Lookup Table Approach, Canadian Journal of Remote Sensing, Vol. 23, pp. 354-368.

Robert O. Green, and Co., An Inversion Algorithm for Retrieval of Atmospheric and Leaf Water Absorption From AVIRIS Radiance With Compensation for Atmospheric Scattering, Jet Propulsion Laboratory, California Institute of Technology.

Palmer, K.F, D. Williams, 1974, "Optical Properties of Water in the Near Infrared", Journal of Optical Society of America Vol. 64, pp. 1107-1110

Staenz, K., T. Szeredi, J. Schwarz, 1998., "ISDAS - A System for Processing/Analyzing Hyperspectral Data", Canadian Journal of Remote Sensing, Vol. 24, No. 2, pp. 99-113

Wessels, G.J.; Buchheit M., Espesset A.; "The Development of a High Performance, High Volume Distributed Hyperspectral Processor and Display System," IEEE International Geoscience and Remote Sensing Symposium and the 24th Canadian Symposium on Remote Sensing, Toronto, Canada, June 24-28 2002