Software tools

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Software tools

SeaDAS extension for turbid waters

The impossibility of obtaining atmospherically corrected data in the Belgian coastal zone due to the failure of the Standard SeaWiFS atmospheric correction algorithm over turbid waters made us have a closer look at this important problem, and we developed an extension to the standard SeaWiFS algorithm. This extension can easily be implemented within the SeaDAS software. The sources are freely provided and can be downloaded from this web site. Installation and usage instructions are provided.

• Brief description
• Download & install
• Instructions for use

Similarity spectrum for turbid waters

The shape of the water leaving reflectance spectrum in the NIR wavelengths is determined largely by pure water absorption and is thus almost invariant. As such, a universal or "similarity" spectrum in the NIR is defined by normalization at 780nm. This similarity spectrum is calculated from seaborne reflectance measurements and is valid over waters ranging from moderately turbid (water-leaving reflectance at 780nm of order 10^-4 or total suspended matter concentration of order 0.3 gm^-3) to extremely turbid waters (water-leaving reflectance at 780nm of order 10^-1 or total suspended matter concentration of order 200 gm^-3). It can be downloaded here (Source: Ruddick et al., 2006). Important applications of the NIR similarity spectrum include atmospheric correction of ocean colour data over turbid waters, quality control of seaborne, airborne, and space borne reflectance measurements in turbid waters.

The similarity spectrum is discussed in full detail by Ruddick et al., 2006 and can be downloaded here.

Total suspended matter algorithm

A generic multisensor algorithm for total suspended matter retrieval in turbid waters was calibrated and validated in Nechad et al., 2010 (may be downloaded at doi:10.1016/j.rse.2009.11.022).

The coefficients A^ρ, B^ρ and C^ρ (respectively A, B and C) established for TSM retrieval from reflectances Rrs, (respectively from backscattering to absorption ratio, b_b/a) to be used in Eq 1 (respectively Eq 2), taken at MERIS, MODIS and SeaWiFS bands or hyperspectrally tabulated from 520nm to 885nm are listed in  tables 1-2, 4-5 (respectively tables WA2-1 to WA2-6), available here.

Eq 1: TSM= A^ρ πRrs/(1 –πRrs/C^ρ) + B^ρ
Eq 2: TSM=A (b_b/a) /(1 – (b_b/a)/C) + B

As discussed in the paper, the coefficients of calibration B^ρ (respectively B) in Eq 1 (respectively Eq 2) mostly reflects in situ measurements errors, and should be set to 0 when the algorithm is applied to a satellite images.