at La Parguera, Puerto Rico

500*900, 100 m pixel size, not georeferenced
scene iss.2013269.0926.124759.L1B.Puerto_Rico.v04.14765.20130926181516.100m.hico.bil, September 26th 2013.
Image courtesy of OSU

work done april 2016

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
I keep digging
until suitable data
become available
BAND    1      2    3     4    5     6     7    8     9    10   11  12   13   14   15   16   17  18   19   20   21   22  23   24   25   26   27    28   
WL        407 418 430 441 453 464 476 487 499 510 521 533 544 556 567 579 590 602 613 625 636 647 659 670 682 693 PAN  842


with NOAA's LIDAR seatruth dataset    PR_BATHY_4M_Mean_NNresample

The data
Unfortunately, this dataset is not georeferenced.

NIR band at 842 nm
radiance artifact
  • NIR may not be used for deglinting
  • all NIR bands are affected

688 nm
shall be used for deglinting
  • see that the lowest radiance is located in the NorthEastern part of this scene

Blue band 7 at 476 nm raw
  • It is quite clear here that a body of very clear waters sweeps Northwards from SouthEast
  • We have to remember here that very clear waters exhibit strong water volume reflectance in the Blue region of the solar spectrum

band 2 at 418 nm raw
  • Waters on the Mayaguez shelf are under influence of coastal waters which spill over and northwards
  • Such waters would exhibit lower water volume reflectance in the Blue region

  • superb image, hardly any glint
  • see that the lowest radiances are located in the NorthEastern part of this scene
  • note the swirl of turbid waters oozing away from the city of Mayaguez
  • note a body of slightly turbid southern waters sweeping northwards
TCC deglinted

LIDAR (rotated)
  • See that areas at depths 10-20 m along the coastline  in the LIDAR image often exhibit significant radiance in the deglinted red band.
  • This cannot be bottom detection, but rather reveals turbidity in the yellow-red range,
    • particularly at La Parguera.

This explains and justifies the details
of the optical calibration below.

RED band at 648 nm, deglinted/smoothed
  • LIDAR data shows that most of these areas at depths 10-20 m along the coastline should be  optically deep for this deglinted red band.  
    • see zoom over La Parguera  where the bottom cannot be detected deeper than ~4-6 m over the innermost shelf.
  • Therefore, what we see is mostly caused by turbidity in the yellow-red range,
Estimating the deep water reflectance Lsw
is going to be an impossible task
  • unless maybe it is done on a local basis
  • using some specific tools in 4SM
  • with some knowledge of the bathymetry, like the LIDAR coverage

Blue band 7 at 476 nm, deglinted
  • Profile Green is shown
  • Turquoise polygon: area for estimating deep water radiance is shown

Profile GREEN
  • Bands at 419, 442, 476, 545 and 694 nm are shown
  • Deglinting: band 26 at 694 nm is used for deglinting
  • Decline: a strong decline in water volume reflectance is observed from West to East
  • Deep waters: between waypoints B1 and B2 of section B, a small area of deep water radiance is sampled. This area was located after close study of the LIDAR data
  • Coastal waters: blue radiances decline abruptly as the profiles reach to the surrounding of Mayaguez city
    • there is an active point source of turbid waters there