Changes between Version 5 and Version 6 of Sensors/Owl


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Timestamp:
Jul 29, 2014 12:53:24 PM (5 years ago)
Author:
mggr
Comment:

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  • Sensors/Owl

    v5 v6  
    11= Specim Owl Thermal instrument =
    22
    3 The Specim OWL is a multiband thermal instrument covering [http://en.wikipedia.org/wiki/Infrared#Commonly_used_sub-division_schemeen.wikipedia.org/wiki/Infrared LWIR] (specifically 7.6 to 12.3 μm) with 103 bands.  In combination with SWIR measurements, this range enables better classification of minerals, particularly silicates.
     3The Specim OWL is a multiband thermal instrument covering [http://en.wikipedia.org/wiki/Infrared#Commonly_used_sub-division_schemeen.wikipedia.org/wiki/Infrared LWIR] (specifically 7.6 to 12.3 μm) with 103 bands.  In combination with SWIR measurements, this range enables better classification of minerals, particularly silicates.  The sensitivity is sufficient to handle sub-zero temperatures and see differentiation (tested to -21C) and is capable of going up to fire temperatures (verified up to 900-1000C with a yellow-hot metal object, and plenty of headroom in the settings still).
    44
    5 As with the [wiki:Sensors/Hawk], the detector technology is [http://en.wikipedia.org/wiki/Mercury_cadmium_telluride Mercury Cadmium Telluride], this time tuned for LWIR rather than SWIR.  This means there may be a number of bad pixels that need to be masked out.  The OWL has also been found to have "blinking" pixels (also called "naughty", as they're not reliably bad), which switch between two different levels during the capture - at the time of writing, these are masked out, though it is hoped that data can be recovered from them in future.
     5As with the [wiki:Sensors/Hawk], the detector technology is [http://en.wikipedia.org/wiki/Mercury_cadmium_telluride Mercury Cadmium Telluride], this time tuned for LWIR rather than SWIR.  This means there may be a number of bad pixels that need to be masked out.  The OWL has also been found to have "blinking" pixels (also called "naughty", as they're not reliably bad), which switch between two different levels during the capture - at the time of writing, these are masked out, though it is hoped that data can be recovered from them in future.  The detector uses a full-frame readout method, so is not suspectible to straylight during readout (as is the case with the Eagle).
    66
    7 In order to calibrate the sensor, a pair of black bodies can be mechanically moved in front of the sensor lens one by one and a capture made.  Under normal operational conditions, this is done automatically at the end of every line, after the autodark (closed shutter dark frames) capture.  The black bodies should generally be set to bracket the temperature range of interest.  The sensor response has been rated as essentially linear.
     7In order to calibrate the sensor, a pair of black bodies can be mechanically moved in front of the sensor lens one by one and a capture made.  Under normal operational conditions, this is done automatically at the end of every line, after the autodark (closed shutter dark frames) capture.  The black bodies should generally be set to bracket the temperature range of interest and can range from about 15C (lower is possible but risks condensation) to 120C.  The sensor response has been rated as essentially linear.
    88
    99The instrument and, more importantly, measurements are vulnerable to water absorption, so a desiccant cartridge is used to maintain conditions internally.  The system (detector and optics) is temperature stabilised
     
    1111The official Specim page can be found at http://www.specim.fi/index.php/products/airborne/aisaowl
    1212
    13 Data quality and calibration/validation reports may be found in the [wiki:Reports] section.
     13Specim's optical calibration was carried out with a range of filters and a rotary stage.  The bands used for calibration were: 32, 41, 76, 112 (out of 120).  ARSF data quality and calibration/validation evaluation reports may be found in the [wiki:Reports] section.
     14
     15The shutter is a "ball type", so forms an effective thermal barrier and may provide a third "emergency" black body (at roughly 15C, non-stabilised) to allow cross-calibration against other flightlines in the event of the other black bodies failing to be captured.
    1416
    1517== Instrument parameters ==
     
    2729|| Max distortion                         || 0.0755mm or 0.0210 degrees or 0.171% ||
    2830
     31Smile distortion is claimed to be neglible.
     32
     33FWHM is as documented in the .hdr files.
     34
    2935Instrument type is "OWL3", serial number is ??????.  The evaluation was made with an objective of type OLEL43, serial number 011402.
    3036
     
    3743As with the other sensors, an ENVI BIL format is used.  The data are stored in raw binary (16 bit) and the metadata in the accompanying .hdr file.  Filenames are of the form `NAME_YYYY-mm-DD_HH-MM-SS.{raw|hdr}`, where NAME is assigned by the operator.
    3844
    39 Black body captures are stored exactly as normal camera data are. Filenames are as above, but prepended with `T1_` or `T2_` depending on which black body was viewed.
     45Black body captures are stored exactly as normal camera data are. Filenames are as above, but prepended with `T1_` or `T2_` depending on which black body was viewed.  Details on the black body set temperatures are stored in the .hdr files.
    4046
    4147== Navigation / timing system ==