Hello, my name is Shintaro.
I’m using SNAP toolbox(SNAP 6.0). I want Remote Sensing reflectance(Rrs) in BOA(=water surface) from OLCI Images by C2RCC processing.
My question is ; which option should I take in the processing parameters in C2RCC ?
I think Output AC reflectances as rrs instead of rhow is good, but I found In the guidline,
Output AC reflectances as rrs instead of rhow Reflectance values in the target product shall be written as remote sensing reflectances and not as water leaving reflectances
what is the difference between remote sensing reflectances and as water leaving reflectances?
If Rrs is selected the output values are divided by Pi. That is the actual difference between remote sensing reflectances and water leaving reflectances is Pi. That’s the simple answer.
You can find more details here:
Thank you very much for quick reply. I appreciate it much.
I understand your answer as
In ocean colour, often the term “water-leaving reflectance” (rho_w) is used instead of Rrs. The difference is: rho_w = pi*Rrs (with related change in units).
Thus, if we selected the option “” Output AC reflectance as rrs instead of rhow", the output will be the rrs.
if the rrs in the option “” Output AC reflectance as rrs instead of rhow" means ABOVE surface reflectance “Rrs”, isn’t it???
※“Rrs” means AVOBE surface reflectance, but rrs means … below or above surface reflectance??
Let me ask simple question.
if we select the option “” Output AC reflectance as rrs instead of rhow",
which do we get reflectance ABOVE or BELOW the water surface?
Yes, it is above the water surface.
More details about the AC and water constituents retrieval is given in this ATBD. It describes the processing for MERIS. But the general approach is the same for OLCI, S2 MCI and Landsat8.
Hello, so if I want BOA (my case is that I am using Sentinel2 L1C images, not Sentinel 3), what check boxes do I have to check? Only “Output AC reflectance as rrs instead of rhow”? Why is TOA deafult? Do I have to remove sunglint somehow from the images before performing C2RCC?
Best regards, Nela
If you want BOA, you can use both rrs or rhow (Lw), the only difference is a pi factor in between them. TOA is not a default, C2RCC performs an atmospheric correction, so what you obtain are reflectances. C2RCC does not remove sunglint, but there are other AC methods that work well on sunglint if you area is severely affected (i.e. Polymer, freely available too).
Thank you very much for the response! Do you know why with rhow I only get some of the bands (not all bands are calculated in rhow?)
I want to calculate rrs ,when I checked all parameters, the process takes long time. I tried by select only the first choice that contains rrs but the results did not contain rrsi i dont knew why .So i tried again by add checked more parameters. My question is which parameters i need to select it if i am interested with rrs to reduce the time of processing. Thank you in advance.