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MODIS Aqua PSF Point Spread Function

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... of adjacent pixel in scan ... For huge clouds, TOA radiances 50 pixels away from cloud will be contaminated up ... Refinement needed for adjacent pixel ... – PowerPoint PPT presentation

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Title: MODIS Aqua PSF Point Spread Function


1
MODIS Aqua PSF (Point Spread Function)
  • Gerhard Meister, OBPG
  • NASA Goddard Space Flight Center
  • (Futuretech Corp.)
  • January 4, 2006


2
Background
  • Ocean color remote sensing imposes very stringent
    requirements on radiometric accuracy of bands
    relative to each other.
  • Stray light effects are very large for bright
    clouds next to dark ocean water.
  • Theoretical solution correction with
    point-spread function (PSF).
  • Problems PSF not well characterized, light
    source intensity sometimes unknown,
    computationally very expensive.

3
PSF definition
Lm (i0,j0) Sij PSF(i- i0,j- j0)LT(i,j) Lm
Measured radiance LT True radiance PSF Point
Spread Function i line index j column index
PSF kernel 25x25 i i0-12, i0 -11,..., i011,
i012 j j0-12, j0 -11,..., j011, j012
4
Available from SBRS
  • LSF (Line Spread Functions) smaller slit, 1
    pixel from either side of slit, dynamic range
    1-10-3, scan and (simulated) track direction
  • NFR (Near Field Response) measurements scans of
    1x10 slit (slit in track direction), up to 100
    pixels to either side of peak, dynamic range
    1-10-7
  • NFR modeling scatter model, certain shape
    parameters, no absolute scale for PSF

5
Creation of PSF
Assume that PSF of adjacent pixel in scan
direction is given by 0.125/0.75 (theoretical
value from Geolocation ATBD) of center value,
adjacent pixel in track direction is 5 (from
LSF)
Adjust center value and scale parameter from
SBRS model (Harvey-Shack) so that NFR
measure- ments are reproduced
6
NFR measurements and model Band 11
7
NFR measurements and model All bands
8
Paper by Qiu et al. on Terra PSF
9
(No Transcript)
10
Aqua and Terra Band 11 with Lcloud/Ltypical20
11
Aqua all bands with Lcloud/Ltypical20 (PSF
size512x512)
12
Aqua all bands with Lcloud/Ltypical from 10-40
13
Same as before, but 10x10 pixel cloud
14
10x10 pixel cloud, band 11 only, different PSF
sizes
15
100x100 pixel cloud, band 11 only
16
Summary
  • Created Aqua PSF based on SBRS model and NFR
    measurements
  • For huge clouds, TOA radiances 50 pixels away
    from cloud will be contaminated up to 1 (even
    after correcting with 101x101 PSF)
  • For 100x100 clouds, radiances will be up to 0.5
    too high after correction with 25x25 PSF (0.2
    for 51x51)
  • For small clouds, radiances can be adequately
    corrected with 25x25 PSF as close as 2 pixels to
    the cloud

17
Outlook
  • Still need to check the model in track direction
  • Refinement needed for adjacent pixel
  • Validate with real data (nLw should look
    better, but more noise is expected)
  • If successful, implement into SeaDAS as an option
  • Work with MCST on Terra PSF derivation/validation

18
Backup slides
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