Changes between Version 14 and Version 15 of Sensors


Ignore:
Timestamp:
Mar 6, 2009 5:07:46 PM (11 years ago)
Author:
mggr
Comment:

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  • Sensors

    v14 v15  
    1313[[Image(all_sensors-cropped.jpg)]]
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    15 
    16 == LIDAR ==
    17 
    18 The Optec LIDAR operated up to 2008 was owned and processed by ULM - see [wiki:Processing/LIDAR].
    19 
    20 In 2008, ARSF purchased an ALS50 (phase II) LIDAR from Leica.  More information is at:
    21  * [wiki:Sensors/LeicaLIDAR/MikesNotes] - Mike's notes on the Leica training course in Aug 2008 (to be digested and turned into real wiki pages at some point in the future).
    22  * [wiki:Sensors/LeicaLIDAR/MarksNotes] - Mark's bullet notes on the Leica training course in Aug 2008.
    23  * [wiki:Sensors/LeicaLIDAR/MashUp] - The digestion of both sets of notes.
    24 
    25 == Specim ==
    26 
    27 You can find a thesis covering the underlying principles of the Specim instruments (Eagle & Hawk) at http://www.vtt.fi/inf/pdf/publications/2001/P435.pdf
    28 
    29 == Hawk ==
    30 
    31 Some details on Hawk's detector from Jukka @ Specim (email 25/July/2008):
    32 {{{
    33 The detector type on Hawk is MCT (Mercury-Cadmium-Telluride),
    34 which means that it's not a CCD that is typically used for VNIR
    35 spectral range.
    36 
    37 The manufacturer's specification for that MCT detector bad pixel
    38 is the following; if the pixel peak responsivity differs more
    39 than +/- 30% from average responsivity, it is considered to be
    40 bad. According to specification less than 2% of pixels should
    41 be bad. In practice that is from 0.3 to 1.0 %.
    42 
    43 The detector is sealed in a vacuum housing. This vacuum "leaks"
    44 very very slowly. As a result of this new bad pixels may appear.
    45 Eventually the vacuum has to be recovered using a special method.
    46 According to manufacturer it may take from 6 months to several
    47 years before this must be done. So far we've done this only for
    48 a single sensor, which had been used already for several years
    49 before that.
    50 
    51 By they way, there are no similar bad pixels on CCD used on Eagle.
    52 
    53 ... response to query from Ben re: frequency of maintenance:
    54 
    55 There is no particular way or time to say when that operation
    56 is due. You will get a hint from additional bad pixels. Also
    57 if the detector temperature is no longer as low as it used
    58 to be that could be an indication of impurity in the vacuum.
    59 
    60 You don't want to try that operation periodically. It requires
    61 sending the system here and disassembly of some parts. After
    62 that that the system must be reassembled and calibrated.
    63 
    64 I'm not expecting your system do be due for that operation yet.
    65 And I understand you are recalibrating the system at the moment.
    66 This means that new calibration file will "recover" most of the
    67 partially appearing bad pixels if any.
    68 }}}
    69 
    70 == Notes of interest ==
    71 
    72 Eagle uses a 1024x1024 CCD, but only the middle ~504 spectral pixels are used in normal operation (representing the range from ~390nm to ~950nm) and is normally spectrally binned by 2 (giving 252 bands).
    73 
    74 However, when used with a band file for "calibration mode", the instrument returns the full data width (i.e. all 1024 pixels).  This must be accounted for in any calibration code. (source: phone chat with Bill, 6/Nov/2007, much amended 30/Jul/2007 following corrections to Mike's interpretation from Bill)