| Calibration of optical properties:
not for beginers!! 
Waters get slightly clearer away from shoreline
| In 4SM, the calibration of the optical properties
is very much the making of the operator,
who now is assisted by an "automatic calibration" process.
With this image, the choice is between: - discarding the image altogether, as it clearly lacks the coverage of optically deep areas where to estimate the deep water radiance in the Blue and also the Green bands:
- this would be advisable in a commercial situation...
- undertaking to set Lsw[1] and Lsw[2] at values which allow for acceptable results (geometry of the calibration diagrams) while making the most of the information that is at hand (modeling as deep as possible):
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The adjacency effect
Adjacency effect is efficiently removed
by the "deglinting "process
- it is hardly noticeable in the blue band
- it is faint in the green band
- it is strong in the red band
- it is even stronger in the NIR band
| must be removed
Lsw[1] and Lsw[2] values are tentatively set
through close inpection of the image
and through calibration
 |
Sea truth
seatruth data courtesy of Sam Purkis, Nova University, Florida |
Sea truth
seatruth data courtesy of Sam Purkis, Nova University, Florida |
39,900 recorded depth points
All modeling parameters have been estimated through the automatic calibration process - the odd results at less than 4 m of computed depth are caused by water being locally more turbid
- depths in excess of 7 m are clearly overestimated, possibly due to uncertain "glint" regression of atmospheric adjacency effect
- a slope of 0.99 demonstrates that
- WL[green]=580 nm for a water type OIII of Jerlov seems appropriate for the Ikonos sensor
|
39,900 recorded depth points
Two-bands case for all pixels
All modeling parameters have been estimated through the automatic calibration process
- by disabling the three bands case, all pixels are now modeled by the blue/green pair only
- this suppresses the problem caused by water turbidity in the red band,
- but also causes all bottom signatures to be shades of grey...
|
Profile 69 and...
modeling by the two-bands case |
...and its seatruth diagram
modeling by the two-bands case |
Six profiles and...
modeling by the two-bands case
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...and their seatruth diagram
modeling by the two-bands case
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