Changes between Version 1 and Version 2 of Processing/atmosphericcorrection


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Timestamp:
Jan 13, 2016 10:40:13 AM (3 years ago)
Author:
mark1
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  • Processing/atmosphericcorrection

    v1 v2  
    99Useful guides to the collection of field spectra for validation purposes:
    1010
     11* [http://fsf.nerc.ac.uk/]
    1112* [http://www.auscover.org.au/xwiki/bin/view/Good+Practice+Handbook/WebHome]
    12 * [http://fsf.nerc.ac.uk/]
     13
     14Please read the above guides as they cover the subject in much more detail than we can here. The following should give a brief summary of general "do's and don'ts", some of which may be obvious but are easy to forget when out in the field.
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     16* Do not stand between the sun and the survey point - you will cast a shadow over the area. Ideally stand as far back as possible so as not to create erroneous reflections.
     17* Measure level, homogeneous targets of greater size than the resolution of the remote sensing data. In most cases this is not possible (even a square metre of concrete is not perfectly homogeneous) but try and find suitable targets. For example an expanse of car park may be suitable, a field of grass, a body of deep water. Surfaces that are not level will suffer greater from erroneous reflections (see bi-directional reflectance distribution fuinction (BRDF)).
     18* Make sure you collect more than one observation over the target to improve the measurement statistics (get as many as possible).
     19* Try to measure near the centre of the targets rather than the edge where possible. For example, if you survey a car park do not observe near the boundary fence or hedge. If observing a water body remember the depth of the bottom will also affect the reflectance (e.g. the shallow boundaries will be different to the deep centre).
     20* Always get an accurate measurement of position (use GNSS / GPS connected to the measurement instrument). You may need to measure the same target for many seconds to get a more accurate position measurement.
     21* Take photographs - they will act as a reminder to the conditions of the day and the targets surveyed.
     22* Measure a mixture of targets - each target will have different spectral responses and you don't want to collect only targets with response in the VNIR (visible near infra-red) range if you are also interested in the SWIR (short wave infra-red).
     23* Use calibrated targets - if you have these available and they are suitable for positioning over the airborne survey site (and suitable for the airborne instruments) then use them.
    1324
    1425== Available software ==
    1526
     27There 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.
     28
    1629=== ATCOR4 ===
    1730
     31Requires a licence and runs in an IDL environment. Specially designed for airborne remote sensing data. ARSF-DAN own a licence for this software and offer an atmospheric correction service to ARSF data users.
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    1833=== 6S and Py6S ===
     34
     35Open source software. Not specifically designed for airborne remote sensing data. ARSF-DAN use this for data quality checks of hyperspectral data.