REFLECTANCE HYMAP DATA - FILENAME CONVENTIONS
This CD contains the HyMap data products, sensor information, and/or
aircraft ephemeris data. All the files have the same root name and an
underscore and additional descriptors, if needed. The root name
indicates the sensor, date of acquisition, and flight, run, and scene
numbers. For example, HyMap data scene 1 acquired on the second run
of the first flight September 29, 1999 has the following root name:
HY - Hymap sensor ID
19990929 - Date of acquisition
fxx - Flight number
rxx - Flight run number
sxx - Scene number (run broken into multiple files,
The following files are provided:
The EFFORT corrected HyMap reflectance data in integer units. To
remove the EFFORT correction, divide the data by the gain values
in the file "rootname"_effort_gainoff.txt.
An ASCII text header file in ENVI format indicating the number of
samples, lines, bands, data type, header offset, interleave, byte
order, X start, Y start, wavelengths, and full width half maximums
An ASCII text file of gain and offset values for applying the
EFFORT correction to the ATREM atmospherically corrected data.
The columns in the file are band number, wavelength, offset
value (set to zero since gain only corrections are performed),
gain value, and error. To remove the EFFORT correction, divide
the data by the gain values in this file. This can be
accomplished in ENVI using the Spectral Math function under the
Spectral Tools menu. First open the EFFORT corrected data file
("rootname"_effort) using "File > Open Image File". Next, import
the gain factors into a plot window by selecting "Basic Tools >
Display Controls > Start New Plot Window". From the new plot
window select "File > Input Data > ASCII..." and select the
"rootname"_effort_gainoff.txt file. Use column 1 for the
X Values and in the "Select Y Column Values" selection box choose
column 3. The gain factors will appear as a spectrum in the plot
window. From the main ENVI menu select "Spectral Tools > Spectral
Math" and enter the following expression:
fix(s1 / s2)
Click OK and assign the variables as follows:
s1 - Select "Map Variable to Input File" and select
s2 - Select the gain spectrum from the Available Spectra List
Output the result to a new file that will contain the reflectance
data without the effect of EFFORT values. The reflectance values
are scaled by 10000.
An ASCII text file of the processing parameters for ATREM.
An ASCII text file of the ATREM output gaseous transmittance
The ATREM output water vapor image.
An ASCII text header file in ENVI format for
An ASCII text file of the band numbers, ATREM input wavelengths,
An ENVI function that converts images in raw input space into
geocoded products. For an example of a geocoded product see
"rootname"_geo. Place this file in the "save_add" directory
of your ENVI installation and then restart ENVI. When you
restart ENVI the option will automatically appear on the menu
under "Utilities > Data Specific Utilities > Hymap > HyMap
Geocorrect from GLT Lookup File". While these images are visually
pleasing and map-correct, they do have several practical drawbacks.
First they have null values (-9999) around their edges that must be
masked in processing. Secondly they are often inflated in size by
replicated pixels as indicated in the "_glt" files. These two
disadvantages lead to our suggestion to acquire and process the
HyMap imagery in its raw spatial format, then apply the
geocorrection to the derived final products.
A true color quick look geocoded data product of HyMap
bands 14(.64), 8(.55), and 2(.46).
When mosaicking geocoded flightlines together, make sure to set
the background value to ignore to -9999. The null pixels around
the images have this value.
An ASCII text header file in ENVI format for "rootname"_geo.
Input geometry file that denotes the UTM Easting and Northing
values derived by the geocorrection process for each original
image pixel. The first band contains UTM Easting values in meters
and the second band contains UTM Northing values in meters for
each original pixel. The input geometry file has the same spatial
size as the raw HyMap imagery. The file is double precision,
binary data in a BIL format. The scene elevation, pixel size, and
UTM zone number information are given in an associated ASCII
header file. The input geometry file itself is not geocorrected,
but does contain the geolocation information for each original raw
An ASCII header file in ENVI format for "rootname"geo_igm.
The geometric lookup table file represents much of the important
information that is created in the geocorrection process. The
"_glt" file contains the information about which original pixel
occupies which output pixel in the final product. Additionally,
it is sign-coded to indicate if a certain output pixel is "real"
or a nearest-neighbor infill pixel. The "_glt" file is a
geocorrected product, with a fixed pixel size projected into a
rotated UTM system. The pixel size, scene elevation, UTM zone
number, and rotation angle information is reported in an
associated ASCII header file. The "_glt" file is two-byte
integer binary data in a BIL format. The two bands of the
"_glt" file refer to original sample number and original line
number, respectively. The sign of the value indicates whether
the pixel is an actual image pixel, located at its proper
position (indicated by a positive value) or a nearest-neighbor
infill pixel placed to fill an undersampled image gap
(indicated by a negative value). A zero value signifies that no
input pixel corresponds to this output pixel. The importance of
the "_glt" image and its role in identifying image gaps and
infill pixels must be stressed, especially for studies involving
small targets. The geometric lookup table file can be used to
geocorrect any band or derived product through a simple lookup
An ASCII header file in ENVI format for "rootname"geo_glt.
The output report file from the AIG HyMap processing pipeline.
The flight acquisition log.
Aircraft ephemeris information for each scan line. The file
contains: line number, UTM X (meters), UTM Y (meters),
altitude (meters), pitch (degrees), roll (degrees), and