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I am trying to distinguish a value for the baseline interpixel variability associated with the background noise of an image.
From what I understand, the pre-launch specifications for MODIS band 1 (645 nm) defined the SNR to be ~130 at L_typ of ~2 mW cm^-2 um^-1 sr^-1. Actual SNR seems to be as high as about 1.5 times that for both Aqua and Terra. This raises two questions:
If Ltyp is ~2, then I am puzzled at seeing maximal values in highly turbid estuarine waters of only ~1, and offshore waters typically < 0.03 mW cm^-2 um^-1 sr^-1 (see attached figure, and associated parameter file)?
Presuming the SNR of 130 does not include noise introduced by atmospheric interference or atmospheric correction, would it be accurate to say that 7.7% (1/130*100%) represents the baseline interpixel variability due to sensor noise and not associated with geophysical variability (oceanic or atmospheric)?
where did you get that number (SNR of 130 prelaunch for band 1) from ?
Since it is a prelaunch number, indeed it should not include geophysical variability.
And I would agree with your calculation of the baseline interpixel variability.
I have seen Ltyp for 640nm for top-of-atmosphere radiances provided as 1.9 or 1.65 mW cm^-2 um^-1 sr^-1. The
value you provide of 0.03 is probably a water-leaving radiance (your plot title 'Lw' does suggest this).
128 for SNR of band 1 is the prelaunch specification. Prelaunch measured SNR is 168 (IEEE TGARS, Vol. 36, No. 4, 1998, pp.1088-1100, Barnes et al.,), on-orbit
measured SNR is about 198 (IEEE TGARS, Vol. 48, No. 1, 2010, pp.535-546, Xiong et al.).
Thanks for that. My L_toa looks far more reasonable wrt to Ltype....