| 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
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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
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