A 1265*1559 subset of Landsat TM_009_045_1990-11-22 at Caicos Bank, Bahamas
Landsat TM_009_045_1990-11-22 courtesy of FUGRO-NPA, from USGS/Glovis
Refer to UNESCO's BILKO project http://www.unesco.bilko.org
Please refer to Bilko Training materials: Unesco's REMOTE SENSING Handbook for Tropical Coastal Management
The BILKO dataset includes a large Sea Truth dataset which extends outside of the tmnov image subset.
Refer to "Benefits of water column correction and contextual editing for mapping coral reefs"
P. J. MUMBY , C. D. CLARK , E. P. GREEN and A. J. EDWARDS, IJRS, 1998 , vol. 19 , no. 1 , 203 ± 210

return to 4SM tutorials  

Work in progress:
upgraded to 4SM.8.02, november 2017

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
updated August 2011, then November 2017
Meet the Caicos Bank TM image and seatruth dataset
A case study in 4-bands modeling,  with sea-truth
A very nice and bright image, no noticeable sky glint,
just very few small clouds or lump of haze, distinct sea grass beds
  • The problems with BILKO's original tmnov 800*900 image subset is that
    • an acceptable calibration cannot be achieved until the whole TM_009_045_1990-11-22 image is calibrated
    • too many seatruth depth points are located outside
    • the coregistration of the seatruth dataset with the tmnov image  -done in the late 80s-  is far from optimal, 
      • quite a number of depth points are located over land
  • This is why we designed
    • a somewhat larger 1265*1560 tmnov subset which suffers none of these problems
      • the pixel size of USGS/Glovis UTM-projected images is 30*30 m
    • a cleaned/verified seatruth dataset with same projection and georeferencing as TM_009_045_1990-11-22 image subset, courtesy of FUGRO-NPA
      • it is called depth_points_reproject
        • (should better be called depth_points_verified, as it it still UTM zone 19)
      • such that the co-registration has been improved to a large extent
from Lesson 4 of the BILKO package
Bathymetric mapping using Landsat TM imagery
  • "The image you will be using was acquired by Landsat 5 TM on 22nd November 1990 at 14.55 hours Universal Time (expressed as a decimal time and thus equivalent to 14:33 GMT).
  • The Turks & Caicos are on GMT – 5 hours so the overpass would have been at 09:33 local time.
  • You are provided with bands 1 (blue), 2 (green), 3 (red) and 4 (near-infrared) of part of this image as the files TMBATHY1.GIF, TMBATHY2.GIF, TMBATHY3.GIF, and TMBATHY4.GIF.
  • These images are of DN values but have been geometrically corrected.
  • The post-correction pixel size is 33 x 33 m and each image is 800 pixels across and 900 pixels along-track
  • .......
Field survey data
  • UTM coordinate referenced field survey depth measurements for 515 sites on the Caicos Bank are provided in the Excel spreadsheet file DEPTHS.XLS.
  • This includes the date, time, UTM coordinates from an ordinary or Differential Global Positioning System (GPS or DGPS), depth in metres (to nearest cm) measured using a hand-held echo-sounder, and DN values recorded in Landsat Thematic Mapper bands 1 to 4 at each coordinate (obtained using ERDAS Imagine 8.2 software).
  • The Tidal Prediction by the Admiralty Simplified Harmonic Method NP 159A Version 2.0 software of the UK Hydrographic Office was used to calculate tidal heights during each day of field survey so that all field survey depth measurements could be corrected to depths below datum (Lowest Astronomical Tide). [Admiralty tide tables could be used if this or similar software is not available].
  • The predicted tidal height at the time of the satellite overpass at approximately 09.30 h local time on 22 November 1990 was 0.65 m (interpolated between a predicted height of 0.60 m at 09.00 h and one of 0.70 m at 10.00 h).
  • This height was added to all measured depths below datum to give the depth of water at the time of the satellite overpass."
==> So that all computed depths <==
should ideally be equal to recorded depths provided.
Tide height at satellite overpass was 0.65 m LAT.

In this tutorial, we shall
  • GRN to BGRN : extend the calibration from a 3-bands image to a 4-bands image: Blue, Green, Red and Nir
  • see that an acceptable calibration can be reached by using only this larger subset
  • establish a set of Ki/Kj ratios for 6 possible pairs of bands in that image: K1/K2 , K1/K3 , and K2/K3 , K1/K4 , K2/K4 and K3/K4
  • see that, in order to specify spectral K for all four wavebands, a seed K value may be introduced
    • either using Kblue/Kgreen, WLblue and WLgreen , and Jerlov's attenuation data for shallow marine waters
    • or using a known operational value for Knir
  • discuss and compare these two methods, comment on "quasi-absolute" optical calibration
  • "deglint" a scatter of very localized and faint lumps of haze
  • run several sea truth tests
  • enquire into operational value for WLblue, WLgreen , and  WLred,
  • compare 4SM modeling with NOAA's Stumpf modeling
  • venture into shallow bottom typing
Get ready

Download   4sm_tutorial tmnov.zip (41 MB) november 2017

  • Move 4sm_tutorial tmnov.zip:
    • "mv       4sm_tutorial tmnov.zip       ~/4SM_tutorials/."
    • "cd ~/4SM_tutorials"
  • Unzip it:
    • "unzip 4sm_tutorial_tmnov.zip"
  • This creates a ~/4SM_tutorials/4sm_tutorial_tmnov directory, with following content:
    • data/............................................TM_009_045_1990-11-22.tif
    • seatruth/......................................various seatruth files
    • shapefiles....................................various shapefiles
    • 4sm.calls....................................directory for various system calls (GMT and shp2text)
    • 4SM.4.08....................................uptodate 4SM executable code, as of end november 2017
    • tmnov.sh.....................................command line script
    • ....................................................various_shapfiles
Get ready
  • "cd  ~/4SM_tutorials/4sm_tutorial_tmnov/data"
    • "openev"
    • export...............................TM_009_045_1990-11-22.tif   
      • into .........................TM_009_045_1990-11-22.pix
    • display color composites in OpenEV
    • check that the following shapefiles are available and overlay to satisfaction
      • ../import.shp
      • ../Lsw.shp
      • ../dLsw.shp
      • ../LsM.shp
      • ../vegetation.shp
      • ../baddata.shp
      • ../glint.shp
    • or make your own
    • "cd ../"
  • check the following are executable
    • "chmod a+x tmnov.sh"
    • "chmod a+x 4sm.calls/*"
    • "4sm.calls/pstext"
    • "4sm.calls/shp2text"
  • "gedit tmnov.sh &"
  • "tmnov.sh"
  • You should be ready for the next step : Prepare your image



tmnov tutorial flow Chart


Just in case you get messed up
For each of the following steps,
you are provided with the specific commandline script
that you can copy to update script tmnov.sh


Prepare your image
           Customize your command line
           Prepare for the AutoCalibration
           and run it

Model 1
           First modeling straight from the AutoCalibration
           Profile 1 : inspect the raw/deglinted radiances
           Profiles : inspect the depth and watercolumn corrected reflectances
Investigate Lsw

Get a License key

Calibration 1 
           Start tuning the calibration diagram for spectral LsM

Calibration 2  
            Secure a wavelength for the Green band : CoefWL for the green band

Calibration 3  
            Some tweaking of spectral LsM and Lw

Calibration 4  
Deglint not needed
             Ghost pixels in calibration diagrams : BPL pixels are not really "spectrally neutral"

Calibration 5

BiDimensional Histograms of marine pixels only
Calibration under a local mask
Customizing the two-bands case : profileAB and RLBgb

Calibration 6


Model 2
Model under a mask

Negative bottom contrast and Water volume reflectance
Lm thresholds
Use the NIR band

Bottom Typing  
              Select specific AOIs and extract their spectral watercolumn corrected bottom signatures
              Improve their representativity through provisional bottom typing
              Run the Classifier for the whole image
              Finish by running the classifier over the outer reef

UseNOAA's RLN method (Stumpf et al, 2003)
And compare both methods

 Congratulations : you're through!!!!