MEASURING DISSOLVED ORGANIC MATTER FROM THE MERIS/ENVISAT SATELLITE

摘要

The special instrument OLCI (Ocean Land ColourrnInstrument) on board of Sentinel 3 is designed for oceanrnand land colour measurements. The experience of sensorrnMERIS/Envisat (The MEdium Resolution ImagingrnSpectrometer) goes back as far as 2002 and will berntransferred to use of new data. Coloured dissolvedrnorganic matter (CDOM) is the main light absorbingrnfraction in many inland and coastal waters and also arnvery important environmental factor in the global carbonrncycle. However, for that parameter there are no goodrnalgorithms over a very high content range. Data from thernEstonian lakes V?rtsj?rv and Peipsi were analyzed withrnMERIS full resolution images from 2008 (42 images)rnalong with in situ measurements from 2008–2011 (totalrnof 407 samples). The processors used for analyzingrnsatellite data were Boreal, Case 2 Regional andrnFUB/WeW. For adjacency effect the ICOL (ImprovedrnContrast between Ocean and Land) processor wasrnapplied. Using in situ measurements and satellite data ofrnthe same day for validation, the best coefficient ofrndetermination R~2 was achieved with Boreal (0.66), butrnthere was also a significant bias. On the basis of theserndata a local algorithm is suggested. The temporalrnvariability analysis of CDOM based on both satellite andrnin situ data showed that CDOM had higher values in thernspring, lower values in the summer and values rise againrnin the fall - that accords to the earlier knowledge aboutrnthese lakes. The spatial analysis based on the 2008–2011rnin situ dataset showed that in average the highest CDOMrnabsorption coefficients (aCDOM 442 nm) were in LakernPihkva (4.6 m~(-1)) and Lake L?mmij?rv (5.7 m~(-1)), in LakernPeipsi s.s. it is 3.1 m~(-1) and in Lake V?rtsj?rv 4.0 m~(-1). Inrnboth lakes the higher values were measured in samplingrnpoints which were near river inflow, showing thatrnCDOM is mostly of allochthonous origin.