How the set-up of the scanner
is naturally dependent on the type of scanner. Whisk broom
scanners will often have a set of predefined bands, of which
a number can be selected, push-broom scanners may have the
option of programming channels by integrating spectral bins.
In the following section the configuration is discussed
based on the assumption of programming a casi scanner as used in this
project. More general recommendations are given in the lower part of the
The configuration element can be split into the interrelated
- Band width and placement
- Spatial resolution
The spatial resolution may limit the number of bands
which can be acquired in a given configuration.
The actual configuration
is very much a balance between spatial resolution, spectral
resolution and the available photons to reach the sensor units.
A high spatial resolution will give a shorter
integration time for each pixel and thus less photons to the sensor.
Narrow spectral bands leads to both low signal to
noise level and thus also to low discriminations levels.
The available radiance from the bottom is determined
by both irradiance, the water depth, the attenuation in the water
column and the bottom reflectance.
In the figure below the absorption of clear water is shown as
the percentage of down-welling radiance just below the surface that is available at different
depths. It is clearly seen that he region with the highest
transmittance of radiance is below 600 nm, and that
practically no radiance from the bottom can be expected for bands
above 700 nm. Remark that the figure shows the maximum available
percentage of down-welling radiance, since other constituents in the
water will further reduce the down-welling radiance at a given
Based on absorption coefficients from Kirk, 1994