We have been investigating the annual/seasonal variability of chlorophyll-a concentration and its relationship with sea-surface temperature and river discharge in coastal shelf region of northern Bay of Bengal (Norther Indian Ocean) and validate MODIA Aqua chl-a data with in-situ measurement. We used 16 years’ level- 3 MODIS aqua chl-a (OCI algorithm) data for our study. But, we are facing several questions related to data from scientific community while publishing paper. The question was quoted below …
“In general, MODIS chlorophyll concentration products provided by NASA were directly used in the paper, without regional correction or regional algorithm inversion, which would lead to the unreliability of the results: It is suggested to carry out regional correction of MODIS or regional algorithm inversion”
How can we clarify this query?
As we worked with level-3 data, there are no way to use regional algorithm. Level-3 chl-a data has a build-in algorithm called OCI (OCx and CI combined). Moreover, there need huge work load (time and funding) to form up a regional algorithm, which was not the scope of our study. Developing regional algorithm can be handy to get more accurate results. But without it, can’t we use level-3 data for our study area in scientific study?
I need some really strong and plausible statements regarding this query? We are rigorously questioned about quality of MODIS aqua data.
The same question I asked the EUMETSAT coordinator, she said that you need to apply a regional algorithm.
Thanks
Dear Muhammad,
All remote sensing data could be unreliable if the assumptions in the algorithm applied are violated in the place where they are used. The concerned with some chlorophyll algorithms (e.g. OC-x) is that they are empirical algorithms based on open ocean data where most parameters covary with [chl]. As one gets closer to shore, suspended sediment and colored dissolved organic matter from terrestrial sources and/or ocean bottom can become important contributors to color whereby the assumptions of the empirical algorithm may be violated. There are other products, such as from GIOP, QAA or GSM inversions scheme that do not make such assumptions and are expected to work better in coastal areas, as they allow for independent variability of [chl] and other constituents. In any case, and as a general rule, it is always advisable to validate remote sensing data with some local data prior to using it for publications. Best, Emmanuel
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