[ back again... :-) ] Nikos wrote:
> > > Downloaded: > > > - extra: LT50160351988258XXX03 (includes visible clouds - maybe good for testing?) Hamish: > in the GloVis preview I only see a few clouds in the NE corner > for that date. (Sept 14, 1988) Right. I specifically selected a scene with a few visible clouds. Isn't this a "good" quality test for the module (instead of using an "easy" scene full with clouds)? > Maybe 1991/10/25 is another good scene for a cloud test? (looks > like 20% high cumulus with shadows) Yep, why not. Will order. > Note the % cloud cover in the GloVis previewer is (AFAIU) using > the same ACCA algorithm as i.landsat.acca, so the result should > be similar. (??) hmmm... have to check. > For the Sept 14, 1998 example the GloVis info says 0% cloud > cover, but maybe that data is old and the latest ACCA says > something else? > > # rgb colors for 742 > > i.landsat.rgb r=lsat5_1988.2 g=lsat5_1988.4 b=lsat5_1988.7 > > strength=96 > > d.rgb r=lsat5_1988.2 g=lsat5_1988.4 b=lsat5_1988.7 # > > obvious clouds > maybe i.landsat.dehaze is worth trying before i.landsat.rgb? > > # toar > > i.landsat.toar band_prefix=lsat5_1988 method=uncorrected \ > > > > sensor=5 product_date=1988-09-14 date=1988-09-14 \ > > solar_elevation=48.6773844 > > do not assume production date is the same as acq. date; check > metadata values against values in the source code. > For the Mar 31, 2000 sample data it made a difference. ok! > > # acca > > i.landsat.acca -5f2 band_prefix=lsat5_1988.toar \ > > output=lsat5_1988.toar.acca > > # how many cats? > > r.info lsat5_1988.toar.acca -r > > min=6 > > max=9 > see r.category, r.stats -c, or d.legend for meaning of category > numbers. (6=cold cloud, 9=warm cloud, 2=shadow) > i.landsat.acca is in flux today, best to wait a few days .. > (some earlier improvements just got clobbered and new ones > introduced, so I'm unsure of where we are now) > > In the "acca" result: > > > > - clouds are detected (cat=6), not that bad(ly) I suppose. > > Some filtering could push away the (rest of the) "noise". > > the cloud despeckle filter can remove some lone non-cloud cells > which are surrounded by cloud. after that I guess it's > r.neighbors or r.mfilter. --%<----- > > - obvious mis-detections (commission errors) found within > > > > - n=188310 s=168270 w=618870 e=636150 (bare ground? > > > > urban area? not sure > > about the confusing land cover/class here...) > > > > - n=219030 s=180510 w=646410 e=655740 (road) > > ? maybe google maps satellite view helps if the landsat is too > coarse to ID features. > > > - in the borders due to the non-identical extent of all bands (!?) > > I've seen something similar, maybe r.series to accumulate NULLs > in all input bands and use that as a MASK? > > > - categories 7 and 8 seem to be empty, category 9 looks > > very messy > > cat 7,8 are undefined, cat 9 probably has more false positives > in warm land, cat 6 (cold cloud) probably has more problems in > snowy areas. > > Could it be that non-cloudy acquisitions are mistreated by > > the algorithm? > > The paper by Irish listed in the i.landsat.acca man page is > worth reading, it explains a lot and points out where the > algorithm does not do well. > > > I can't clearly recognise clouds in the landsat > > scenes included in NC data set > > (both the 1987 and the 2000 scenes). > > I'd guess that they were specifically chosen to avoid days with > obscuring clouds. > > > Will (then) the algorithm work (only) with (very) cloudy > > data? > > One thing the paper mentions, and I've observed, is that it does > not do well with thin wispy cirrus clouds. Apparently MODIS does > a bit better there because it has a detector in the needed 2um > range to pick those up, while the Landsat only has 11um which > misses those cloud tops. (IIRC) --%<----- Will check the above at some point. > fyi, I've just added what we know about the NC 2008 dataset > Landsat images to the grass wiki: > http://grass.osgeo.org/wiki/LANDSAT#Sample_data Thanks, Nikos > I'm downloading them now.. I expect they'll be reprocessed > versus the metadata calibration values shipped with the dataset. > (??) > Hamish _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user