Bathymetry and water column correction
at Mulroy Bay, Ireland
Image courtesy of the U.S. Geological Survey
Using the Panchromatic band for water column correction
to derive water depth and spectral bottom signature:

Landsat 8 OLIP bandset used for this work
Purple=1Blue=2Green=3PAN=4Red=5NIR=6 and SWIR1=7

Work done july 2018
GSD 15 m
See March 27th 2018


GoogleEarth in November 2017

1300*1300 import area



Location of Profile_RED

I want a display of the panchromatic band,
resampled to 2 m GSD


This profile by Massimo exhibits pure adjacency effect

To be honest,
I should first get used to PLEIADES data
over the Bahamas,
where shallow bottoms are very bright,
and waters very clear.

First thing first: estimate spectral deep water radiances
  • Deep water reflectances increase steadily from North to South
  • Red band exhibits turbid waters all along the waterline, particularly at import ROI
After considerable hesitation, and in view of the modeling results,
a bold compromise is finally adopted: Lsw/194.0/148.3/97.0/95.4/34.6
and a conservative threshold for the Red_solution: -Lm/1.0/1.0/1.0/5.0/255.0
Warning: not for beginners


that's up North
LSW 194.0 148.3  97.0  95.4  34.6

that's down South
All deep water reflectances are much lower  

Something happens between 0 and 400 m:
waters clearer??

Back to normal
keeps decreasing steadily southward

PANchromatic band

With PANchromatic band
  • PAN in channel_3 is quite noisy:
    • resampling from 0.5 to 2.0 m GSD involves averaging over 16 DNs, so should be ultra-smooth, right?
  • Then we shall see that PLEIADES's PAN response curve is not suitable for 4SM modeling

The following parameters were used
Band.....1........2....PAN..... 4........5
  • Circular smoothing kernel : 81 pixel
  • That's a radius=5
  • This results in a ~20 m GSD 
  • No Smart_Smoothing here!
  • So much for the 2 m GSD
  • Beach: Lines 4000, 5000, and 6000: the beach features well
    • I have specified a scaling factor so as to obtain a DN brightness of ~250 over the beach
  • all NIR profiles appear to exhibit distinct atmospheric adjacency effect
    • glint regressions have been estimated over optically deep waters:
      • from Row_3300 to_Row_3600
      • from Line_2800 to Line_3200
    • they appear to be acceptable, in spite of noise
      • except for the Red band

  • Lswred has been boosted by 4 units for all profiles
    • in order to achieve acceptable transition from Red_solution to Green_solution
    • this points to water turbidity all along the waterline
  • Even that is not enough at Line_100
    • depth retrieved by the Red solution is strongly under-estimated
    • I  supect stronger water turbidity by suspended particles in the vicinity of Line_100
  • This precludes the use of the Red band for modeling:
    • the Green solution shall be used at all shallow pixels,
    • unless maybe on a local basis
  • I was hoping that the PAN solution would save our day,as it usually does when using Landat_8 or WorldView_2: alas, it is useless for us!


Créer un site
Créer un site