Bathymetry and water column correction
WorldView 2 image Princess Cays, Eleuthera island, Bahamas

  November 11th 2011, 2 m ground resolution
image from Digital Globe
"(c) DigitalGlobe, Inc. All Rights Reserved"
"Includes copyrighted material of DigitalGlobe, Inc., All Rights Reserved"
work done in 2012, 2013 and 2014

The "PAN solution"
uses the PANCHRO bans, 4*4 sum-aggregated and co-registered

bands 1, 2, 3, Panchro, 4, 5, 6, 7 and 8       become      bands 1, 2, 3, 4, 5, 6, 7, 8 and 9

home

This dataset from Digital Globe, under a "Data Exchange Agreement"
Courtesy of Gregory Miecznik

Watch bathymetry webinar presentation by Gregory 2013
 

Please refer to:

    * Towards Deeper Measurements of Tropical Reefscape Structure Using the WorldView-2 Spaceborne Sensor, Antoine Collin and James L. Hench, Remote Sens. 2012, 4, 1425-1447

    * A novel spaceborne proxy for mapping coral cover, Antoine Collin , James L. Hench, Serge Planes, Proceedings of the 12th International Coral Reef Symposium, Cairns, Australia, 9-13 July 2012
For other 4SM investigations using the panchromatic band: see the following


 
1 - NO NEED for field data, nor for atmospheric correction
2 - this is demonstrated in this website, using a variety of hyper/multi spectral data
 
Requirements are
1 - homogeneous water body and atmosphere
2 - some coverage of optically deep water
3 - some coverage of dry land
 
Problems are
1 - the precision on estimated depth is found wanting, because the noise-equivalent change in radiance  of accessible data is too high for shallow water column correction work 
2 - radiance data should be preprocessed by the provider at level 1 in order to improve S/N ratio
3 - exponential decay: the deeper/darker the bottom, the poorer the performances
 
So
I keep digging
until suitable data
become available
 





The data:
this is a new dataset from DG:
This new subset is located to cover existing seatruth bathymetry
It includes a 4*4 sum-aggregated, 2 m resolution, co-registered Panchromatic band

TCC

PAN
  • 4*4 sum-aggregated, 2 m resolution
  • PAN exhibits much deeper penetration than Yellow

Blue
  • Blue exhibits same penetration as Green, although Kblue is ~=0.5 * Kgreen
  • This is because of a very steep drop in bottom depth which is observed throughout the Bahamas

Green
  • Green only exhibits slightly deeper penetration than PAN channel




 

Glint Regressions

Glint regressions based on NIR2 band 9

Note that band 9 is well correlated with all other bands


 

Glint regressions based on NIR1 band 8

Note that band 8 is well correlated with all other bands

 
 


Adjacency effect

Adjacency effect at 908 nm
is still significant ~600 m seaward
Location of profile is shown


 

Removing the adjacency effect
through "deglinting"  appears to work quite well,
including for Panchro band_4

 


   

Optical calibration
Jerlov's water type OIB

Calibration diagram
for bands Blue, Pan, Yellow and Red
  • PAN band exhibits bottom penetration down to 33 m over very bright bottoms
  • this is ~17 m less than the GREEN band
  • and ~55 m less than the BLUE band

 

Calibration diagram
for bands Blue, Green, Yellow and Red
  • GREEN band exhibits bottom penetration down to 48 m over very bright bottoms




 
Operational wavelengths
  • -WL/0427.0/477.5/546.0/570.0/607.5/679.0/724.0/831.0/908.0
  • WLgreen   is set at 546 nm
  • WLyellow is set at 607 nm
  • WLred      is set at 679 nm
  • WLpan     has no meaning
  • At Princess Cays
  • -SCL/95/107/167/2500/171/116/166/164/149
 
  • At Marmion
  • -SCL/55/74/114/2000/104/96/104/118/78


 

Image brightness
Scaling factors from WV2_U16 into U8 for the brightest shallow bottom type
Coral sands at PrincessCays is recorded definitely brighter than calcarenite sands and shell debris at Marmion
Time in the year is that different
But latitude is 8 degrees lower at PrincessCays: that would appear to make a huge difference
Marmion : Western Australia
32° South in june: this is end autumn
Princess Cays: Bahamas
24° North in november: this is autumn
SCL   0.464 0.345 0.224 0.013 0.245 0.266 0.245 0.216 0.327
Imaging in december/january would be optimal
SCL   0.268 0.238 0.153 0.010 0.149 0.220 0.154 0.155 0.171
Imaging in June/July would be optimal