Hi. I am trying to compare combined MODIS and SeaWiFs water quality data with runoff dataset of 0.5 degrees. I am going to use the Level 3 mapped data provided by the NOAA database.
I am particularly interested in the pixels that are near the coast. Is it necessary to regrid the water quality data to 0.5 degrees, or just simple aggregation will do, or lastly, just extract representative pixels from SeaWiFs and MODIS and compare with the larger runoff grids? Are there any similar published journals that I can use as reference?
Thank you very much for the response.
Comparing data should use similar resolution. 0.5 degree is very coarse resolution for water quality assessment anyway. It might be OK for some policy applications. I recommend resampling to same resolution and validate with other observations to improve confidence in your data.
Hi Timothy O Randhir , thank you very much for the answer. I am interested in temporal and spatial patterns on the national scale, hence the coarse resolution.
Yes I am looking into resampling the water quality data to 0.5 degrees. However, I thought that doing so will also remove seemingly outlier temporal patterns that might be provided by some pixels due to localized differences. Level 3 mapped MODIS and SeaWiFs both have 9km resolutions. I was thinking to select only representative pixels near the coast and compare with the 0.5 degree runoff data. Is it a usual practice, or regridding them is the proper way to do it?
The lower resolution data may be up-scaled for comparison. I am agree with Randhir..
In general, you want to indeed re-grid and conduct the comparison with both data sets at the same resolution, and preferably, the re-grid would use a similar or same gridding scheme. The coarser grid set is normally the limiting factor, unless you have the original data so you could regrid the data to a finer resolution. SInce you are interested in coastal feature that may not be that well resolved in the coarser resolution set (subgrid features), you may consider downscaling.
Related papers: you can download view from my RG profile JGR 2013 paper (Patoux & Levy: Space-time interpolation of satellite winds in the tropics) and earlier papers referenced there.
hi, if there is I don't know is what I can inform you at the moment
As already mentioned by others, the image pixels must be resampled so that they have the same spatial resolution. Thus, the grids will be matrices of equal size and can be compared.
Another factor to consider is the radiometric resolution of datasets. MODIS has 12 bits, SeaWiFS has 10 bits. Therefore, it is important to standardize them to the same radiometric resolution (suggestion: 8 bits for both).
In addition, another issue that may influence the comparison between these datasets is the difference in days between images (if any), as there may be variations in radiation intensity and cloud presence. In this case, I suggest applying, before comparison, a linear filter (may be 2%) to minimize the influence of more discrepant pixels due to these aspects.
Good luck on your research.
Hi,
Obviously, the resolutions are different.
You could ;
1. Regrid the resolution of the 9km resolution to 0.5 degree'.
2. Downscale 0.5 degrees to 9km grid cell since you are working on coastal areas. I think this should be able to represent the local features to some certain extent.
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