Looking for time-averaged Monthly chlorophyll-a estimations for Lake Apopka, FL

[sjedmundsonpnnl]

Hi,
I am very new to this area and hoping to learn how to get time-averaged values (e.g., monthly basis over several years), although even just a figure for 2022 would be fantastic.
Lake Apopka, FL is a target, other large hypereutrophic lakes are of interest and would work for the effort. Thanks for your help getting started on this!

[GES DISC - jimacker]

Hello,

You can get this from the Giovanni system, https://giovanni.gsfc.nasa.gov/, but you must input the geographical coordinates for the bounding box around the lake. I just attempted to do this, and I will provide the URL, along with a couple of images to show where the resulting data are located. You can use Giovanni to construct a monthly time-series using these bounding box coordinates. The data in Giovanni are acquired from the OBDAAC and are Level 3 MODIS-Aqua data at 4 km resolution. Because this is inland data for a relatively small water body, there are questions of data accuracy which would be better answered by a specialist. However, Lake Apopka is large enough to provide data. To make the images, I downloaded the netCDF file from the Giovanni results, and visualized it with NASA Panoply. I was hoping Panoply had a map overlay that showed Lake Apopka, but Lake Okeechobee was the only lake large enough to be shown in the overlay file.

URL: https://giovanni.gsfc.nasa.gov/giovanni/#service=TmAvMp&starttime=2022-07-01T00:00:00Z&endtime=2022-07-31T23:59:59Z&bbox=-81.723,28.555,-81.544,28.684&data=MODISA_L3m_CHL_Mo_4km_R2022_0_chlor_a

On the interface, if you click the "folded map" icon in the region selection field (next to the coordinates), you can see where the bounding box is located. The current setting for the interface is to create a time-averaged map for July 2022, so it is only showing one month of data. The Level 3 monthly data provides the averaged value of all the observations that MODIS acquired during the month. You could average all the monthly data for the entire year if you wanted to, but you can also make an area-averaged time series by clicking on the down arrow in the "Select Plot" menu at top left, and then selecting "Time Series, Area-Averaged". I made a time-series for 2022 as well.

MODISA_L3m_CHL_Mo_4km_R2022__in_Lake_Apopka_July_2022_zoom.png (39.13 KiB) Not viewed yet

MODISA_L3m_CHL_Mo_4km_R2022__in_Lake_Apopka_July_2022.png (43.53 KiB) Not viewed yet

MODISA_L3m_CHL_Mo_4km_R2022__in_Lake_Apopka_July_2022_zoom.png (39.13 KiB) Not viewed yet

[GES DISC - jimacker]

I accidentally attached the "zoomed in" map twice.

[sjedmundsonpnnl]

Hi GES DISC - jimacker,

Thanks for your lightning-fast response and walk-through help!! This is awesome!
I think I am finally understanding the GIOVANNI system.

Is the MERIS 300m resolution data set available through GIOVANNI?
Such as described here by Seegers et al. 2021 https://doi.org/10.1016/j.rse.2021.112685: Satellites for long-term monitoring of inland U.S. lakes: The MERIS time series and application for chlorophyll-a

Higher spatial resolution would significantly improve the resolution for many, many smaller lakes (Lake Apopka is quite large, relatively). The best I can see on GIOVANI is the 4km, which you used in your walkthrough. Any suggestions?

Thanks Again!

[GES DISC - jimacker]

The only chlorophyll data we are set up to support in Giovanni is the MODIS-Aqua Level 3 data product. To get higher resolution data from MERIS, VIIRS, or OLCI, you would have to contact the data provider. I hope you will be able to use Giovanni effectively.

[OB SeaDAS - xuanyang02]

OB.DAAC provides L3 mapped files with 4km and 9km resolution, but you can make your own L3 mapped files with higher resolution using SeaDAS -- https://seadas.gsfc.nasa.gov/

1. download L2 files with the desired time and area from OB.DAAC -- https://oceancolor.gsfc.nasa.gov/cgi/browse.pl?sen=amod
2. do l2bin/l3mapgen (SeaDAS science processors) to make your own l3mapped files with the desired resolution.
https://seadas.gsfc.nasa.gov/help-8.4.0/processors/ProcessL2bin.html
https://seadas.gsfc.nasa.gov/help-8.4.0/processors/ProcessL3mapgen.html
3. Use SeaDAS' time series tool
https://seadas.gsfc.nasa.gov/help-8.4.0/timeseriestool/TimeSeriesManager.html

[OB SeaDAS - knowles]

To get down to 300m resolution for MERIS you could download the level-2 files here:
https://oceancolor.gsfc.nasa.gov/cgi/browse.pl?sub=level3&per=CSTM&day=12692+3014&prm=CHL&set=10&mon=12723&sen=mefr&rad=0&frc=0&n=28.684&s=28.555&w=-81.723&e=-81.544&cn=30.07&cs=28.48&cw=-81.91&ce=-80.48&dnm=D

Then click "Find swaths"

But that's nearly 800 level-2 files which you would then need to bin into monthlies.

The relevant SeaDAS tools (as mentioned above) are l2bin and l3mapgen (and possibly l3bin).