Changes between Version 1 and Version 2 of Processing/atmosphericcorrection

Jan 13, 2016, 10:40:13 AM (7 years ago)



  • Processing/atmosphericcorrection

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    99Useful guides to the collection of field spectra for validation purposes:
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    1112* []
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     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.
     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.
    1425== Available software ==
     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.
    1629=== ATCOR4 ===
     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.
    1833=== 6S and Py6S ===
     35Open source software. Not specifically designed for airborne remote sensing data. ARSF-DAN use this for data quality checks of hyperspectral data.