Geoscience Reference
In-Depth Information
The OTB tool,
otbcli_OpticalCalibration
provides a compact tool
to correct optical satellite for atmospheric effects for the DigitalGlobe sensors
(Quickbird, Ikonos, WorldView, GeoEye), ADS VHR optical (Pléiades 1A/1B,
SPOT 6/7) and SPOT5. With the release of OTB-4.2, the tool will become more
generic in so far as the calibration parameters will be exposed through the com-
mand line and filled by metadata parsing. This will mean that previously unsup-
ported sensors can be processed provided the calibration parameters are known. The
otbcli_OpticalCalibration
converts pixel values stored as digital numbers
to calibrated values referred to as surface reflectivity that are stored in the range from
0,1. It provides two levels of calibration:
1. Top of Atmosphere (TOA), which is the most common form of radiometric
calibration that takes the sensor gain, sensor spectral response and solar illu-
mination into account;
2. Top of Canopy (TOC) reflectivity takes the above mentioned image data as well
as additional physical measurements of the atmosphere that include the optical
thickness of the atmosphere, pressure, amount of water vapour, ozone and aerosol
gases.
To correct the imagery to TOC, it is necessary to provide atmospheric parameters
specific to the location and time of image acquisition of your satellite imagery. This
information is rarely provided as metadata with your data, so it is necessary to either
retrieve the information frommeteorological data providers (assuming these data are
collected and available by them) or fromtheAerosol RoboticNetwork (AERONET).
7
AERONET is joinly managed by NASA and French scientific laboratories: PHO-
TONS (PHOtomtrie pour le Traitement Oprationnel de Normalisation Satellitaire),
Univ. of Lille 1; CNES, and CNRS-INSU.
otbcli_OpticalCalibration
provides a facility to either enter in the atmospheric parameters as command line
arguments or to provide an AERONET file, which can be downloaded from the web-
site for a network of measurements sites around the world. However not all sites
contain complete, up-to-date measurements. The command's help is printed below
and lists the range of options that can be entered.
-progress
<
boolean
>
Report progress
-in
<
string
>
Input (mandatory)
-out
<
[pixel] Output [pixel=uint8/uint16/int16/uint32/int32/float/double]
(default value is float) (mandatory)
-ram
<
string
>
int
32
>
Available RAM (Mb) (optional, off by default, default value is 128)
-level
<
string
>
Calibration Level [toa/toc] (mandatory, default value is toa)
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