Changes between Version 9 and Version 10 of Processing/atmosphericcorrection

Timestamp:

Apr 13, 2017, 9:51:04 AM (8 years ago)

Author:

dac

Comment:

Added Gary's text on target placement

Processing/atmosphericcorrection

@@ -45 +45 @@
 * Measure the white reference often (every other measurement).
 
+**Calibration Targets**
+
+NERC-ARF and FSF have calibration targets available for use. When laid out the targets should be approximately 8 x the ground pixel size.
+
+With positioning the targets there are a few things that need to be considered.
+
+* The targets should be separated by approximately the same dimensions as the target, if not greater.
+* The targets should be configured to avoid them being in line with each other (as the aircraft flies, i.e., in the same scan line). The image below shows the arrangement of targets in Barrax 2015 and illustrates this point, note the white target 'bleeds' into adjacent pixels.
+* The white target normally needs a black target underneath it to prevent the underlying surface from showing through. Ideally this target should also be the last in any sequence so that any saturation effects (with subsequent recovery of the detector) do not impact other targets.
+* Adjacency effects are key. The large targets should minimise this but it becomes relevant for small targets. This is the impact of a strong spectral signal at the edge of the FOV. A classic example is vegetation. The effect can be minimised / eliminated if the targets are placed on a spectrally inert surface. Asphalt is normally quite good. Of course this needs to be spectrally inert for all the bands which you wish to use.  
+
 == Available software ==
 
 There are a handful of software packages that offer atmospheric correction but few that specialise for airborne / low to mid-atmosphere cases. There are papers written which show comparisons between various packages used over the same scene. The below software are used by NERC-ARF-DAN.
 
+=== ENVI ===
+
+Commercial general purpose image processing software. Within ENVI functionality is available to perform an empirical line calibration using ground targets. NERC-ARF-DAN are currently working with FSF on producing a guide for this.
+
 === ATCOR4 ===
 
-Requires a licence and runs in an IDL environment. Specially designed for airborne remote sensing data. NERC-ARF-DAN own a licence for this software and offer an atmospheric correction service to NERC-ARF data users.
+Software for atmospheric correction using a Radiative Transfer method, based on the MODTRAN model. Specially designed for airborne remote sensing data. Requires a licence and runs in an IDL environment.
+
+NERC-ARF-DAN own a licence for this software and offer an atmospheric correction service, please contact us for more details.
 
 === 6S and Py6S ===
 
-Open source software. Not specifically designed for airborne remote sensing data. NERC-ARF-DAN use this for data quality checks of hyperspectral data.
+Open source software for Radiative Transfer modelling. Can be used to model atmospheric effects on ground spectra. NERC-ARF-DAN use this for data quality checks of hyperspectral data.