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+--- Thread: Chlorophyll (/thread-37.html)
Chlorophyll - Polaris1 - 2019-07-25
Hi, and please,
1- I am a sailer, and I am confused on which " Current '' should I consider following? Various currents are being displayed
on " GlobCurrent portal ", on the same location!
2- I was wondering How I May I request CHLOROPHYLL file, so as to view it on marine softwares.
or else, is chlorophyll displayed on " GlobCurrent portal " ? I can't see it.
3- The data displayed is always one day behind. Is there a way to request, and try, "today's" data?
RE: Chlorophyll - Lucile Gaultier - 2019-07-29
Hi,
I will assume in my explanation below that you don't know about ocean data, I hope it is not too simplistic.
First, GlobCurrent is a project that aims at improving our knowledge of ocean surface current using remote sensing data. Thus all the products processed within this project are derived from satellite observation, though there is no direct observation of the total current using satellite yet.
1- All the GlobCurrent currents are derived from satellite observation and thus only the previous day observation will be available at best. There are three different kind of Current on GlobCurrent portal:
a- Geostrophic current is computed by averaging all available altimeter satellite on period of 15 days. It is thus low spatial and temporal resolution current that does not evolve much from one day to another
b- Ekman current is derived from the wind (using a parametrisation) and thus will evolve slowly from one day to another
c- The Total current corresponds to the sum between the Ekman and the Geostrophic
Note that there has been a change of provider for this Near Real Time Data. To get very recent data, you should select (CMEMS) product and not the (GlobCurrent) one. Also only the Total and the Geostrophic current are available with the new CMEMS provider, but those are the one you should be interested in for sailing purposes.
A fourth type of data is also available in this portal though not processed within the GlobCurrent project which is Surface current Mercator (1/12).It is derived from a model at higher resolution than the GlobCurrent observation, but contains uncertainty due to the model (front and eddies are not always well located). It can be compared with the Total current from GlobCurrent or CMEMS.
Note also that the Total current is lacking the tide and wave induced components.
2- Chlorophyll data can be downloaded from several providers depending on the sensor. MODIS and VIIRS sensors are hosted by NASA, and can be downloaded on the oceancolor portal (https://oceancolor.gsfc.nasa.gov/), OLCI sensor is part of ESA program and data are available on the scihub (https://scihub.copernicus.eu/dhus), it is part of Sentinel-3A/B satellites. These data are in netCDF and not straightforward to read and thus are not compatible with marine software (which are mainly able to open GRIB I think). I know that the marine software OpenCPN had a project to read netcdf files but as far as I am concerned, this plugin is still under development.
There is no real time Chlorophyll observation on GlobCurrent portal, It will come in few months. You can check on Sentinel3 portal the OLCI OceanColor RGB level1 product that are already available (s3view.oceandatalab.com), there is also high resolution Sea Surface Temperature (SST) from the SLSTR sensor (~1km).
3- There is not much we can do regarding the availability as there are observation. There is a 6h delay for the Sentinel 3 data (OLCI RGB, SLSTR Sea Surface Temperature, and soon Chlorophyll-a), and at least a day for the different currents as it is an indirect observation and thus we need different remote sensing data to compute it.
Icing on the cake: You have much more data available on the OVL portal (ovl.oceandatalab.com) eventhough it can be quite complex to understand as it has been made for ocean scientist. If you are interested in high resolution ocean features, have a look at Sentinel-2 True Color (ESA, Sinergise) and Sentinel-2 Color Infra Red (EAS, Sinergise) products. They are currently unavailable but I hope the data provider will fix this issue very soon.
Let us know if something is not clear to you,
We are really happy to know that people other than oceanographers are using our portals. As a sailor I am also using our portals a lot to study currents pathways, wave direction and breaking, wind patterns and ocean temperature before sailing in a new area.
RE: Chlorophyll - Polaris1 - 2019-07-31
Hi Lucile,
I just cannot express my gratitude and joy while reading your response. It is reminiscent of those university-lectures. Thank you.
I will re-examine, and follow, your succinct explanation, (as being a double EE major,) and would be pleased to return to you for other requests.
Regards.