Dear Nikos, Thank you very much for detailed answer and references! I know the documents from usgs web site, though I was afraid I could miss some important information...
Such a way, this warning is not meaningful in the case of Landsat 8 OLI sensor imagery, if so can this warning be removed in latest Grass versions not to frighten the beginner users? Kind thanks again, -- Best regards, Maria V. Kozlova /------------------------------------\ Information System Lab. (ISysLab) State Oceanographic Institute, Kropotkinsky per., 6, MOSCOW, 119034, RUSSIA ------------------------------------ tel. +7 499 246 6448 fax. +7 499 246 7288 mailto: [email protected] \------------------------------------/ 26.05.2015, 13:40, "Nikos Alexandris" <[email protected]>: > Kozlova Maria: >> Dear colleagues, > > Hi Maria, >> I'm working with Grass Gis 6.4.4. and 7.0 (GUI interface). I calculate >> TOA-reflectance with i.landsat.toar module. But some time I launch the >> module, the following warning appear. >> >> WARNING! ESUN EVALUATED FROM REFLECTANCE MAXIMUM BAND > > Please read the "On Landsat-8 metadata file" section in i.landsat.toar's > manual. The manual explains how it compensates for the not-provided ESUN > values > for Landsat8 imagery. Hopefully this answers all of the following questions. >> Some of my colleagues are sure that I shouldn't pay any attention to this >> warning as the output TOA-reflectance data is always the same with the data >> obtained by entering ESUN value for many routine kinds of work. Although >> they are not sure that it is acceptable for any special image processing, >> such as DOS atmospheric correction etc. And the problem is that my research >> concerned with many experiments of various image processing to get >> acceptable results. >> >> And so I need reliable TOA reflectance data. >> >> My question are: >> >> 1. Can anyone tell if I can get appropriate TOA-reflectance data without >> entering Esun value? Can this parameter significantly influence the output >> data? In what cases? > > But where is the user required to enter it? It is fetched/computed from the > other metadata (from the corresponding metadata file of the acquisition). I > think the ToA-Reflectances derived by the module are appropriate. > > ( > ESUN is the mean solar exoatmospheric irradiance for a given spectral band. It > is part of the formula converting radiance to (planetary) reflectance. Its > calculation involves the relative spectral response of a band and the solar > irradiance over wavelength [0]. Thus, it significantly contributes to the > output data. > > As far as I know, it is required for the conversions of data from most sensors > (Landsat 4, 5 & 7 [1], QuickBird2, IKONOS, WorldView -- yet, not for Landsat8 > [2]). > > ) >> 2. How can I enter Esun value in i.landsat.toar module? > > You can't. Not sure for ETM+ data though, if you could do anything different > via the `gain=` option. Normally you should use the provided metadata. >> 3. Why the warning appear not every time but after the same actions and it >> depend on certain image (problem occur mostly with Landsat OLI images)? > > The "official" OLI conversion formula does not require it. Please read more at > [2]. Thus, they don't provide these values. > > However, the i.landsat.toar module requires it in order to apply well > known conversion formulas, as well as the simple DOS atmospheric correction > methods. And, it gets these values by assuming that the provided maximum > radiance corresponds to the provided maximum reflectance and some math. > > Nikos > > [0] For example, for IKONOS bands see > https://apollomapping.com/wp-content/user_uploads/2011/09/IKONOS_Esun_Calculations.pdf > [1] > http://landsathandbook.gsfc.nasa.gov/pdfs/Landsat_Calibration_Summary_RSE.pdf > [2] http://landsat.usgs.gov/Landsat8_Using_Product.php _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
