Annekatrien, I am doing my first steps with i.atcorr now. I have added (with support from Yann Chemin) the specs for IRS 1C LISS which I need for a project. Also did some manual cosmetics.
To warm up, I am doing first tests with the North Carolina test data set [1] which contains sample LANDSAT 7 data at reduced size. I observe that the module (or the procedure) is pretty slow, perhaps 5 pixels/second on my 2.5GHz box... said this, some comments below: On Fri, Jan 30, 2009 at 6:01 PM, Annekatrien Debien <[email protected]> wrote: > Hi all, > > I want to do an atmospheric correction of my Landsat ETM+ images using the > i.atcorr module in Grass 6.3 on Ubuntu, but I never get an output. what does that precisely mean? It keeps you at 0% and calculates or it exists and no output? With NC data, I get (I hope I got the icnd.txt file right): # set region: g.region rast=lsat7_2002_10 -p # get central scene LatLong coordinates: g.region -gb | grep ll_c ll_clon=-78.70014170 ll_clat=35.71092005 cat icnd.txt 8 - geometrical conditions=Landsat ETM+ 5 24 15.50 -78.700 35.710 - month day hh.ddd longitude latitude ("hh.ddd" is a decimal hour GMT) 2 - atmospheric mode=midlatitude summer 1 - aerosols model=continental 50 - visibility [km] (aerosol model concentration) -.600 - target at 600m above sea level -1000 - sensor on board a satellite 61 - 1th band of ETM+ Landsat 7 To be sure about the time (Landsat overpass, North Carolina is UTC-5): http://earthobservatory.nasa.gov/MissionControl/overpass.php # zoom to be faster for a test d.zoom # We can check the sun position with r.sunmask: r.sunmask -s --v lsat7_2002_10 out=dummy year=2002 \ month=5 day=24 hour=10 minute=30 sec=0 timezone=-5 Using map center coordinates: 636732.750000 217569.000000 Calculating sun position... (using solpos (V. 11 April 2001) from NREL) 2002.05.24, daynum 144, time: 10:30:00 (decimal time: 10.500000) long: -78.700150, lat: 35.710922, timezone: -5.000000 Solar position: sun azimuth: 117.002434, sun angle above horz.(refraction corrected): 63.261234 Sunrise time (without refraction): 05:08:34 Sunset time (without refraction): 19:15:46 No map calculation requested. Finished. # do the correction i.atcorr lsat7_2002_10 ialt=elevation icnd=icnd.txt \ oimg=lsat7_2002_10_atcorr * ****************************** 6s version 4.2b ****************************** * * geometrical conditions identity * * ------------------------------- * * etm+ observation * * * * month: 5 day: 24 * * solar zenith angle: 26.71 deg solar azimuthal angle: 117.09 deg * * view zenith angle: 0.00 deg view azimuthal angle: 0.00 deg * * scattering angle: 153.29 deg azimuthal angle difference: 117.09 deg * * * * atmospheric model description * * ----------------------------- * * atmospheric model identity : * * midlatitude summer (uh2o=2.93g/cm2,uo3=.319cm-atm) * * * * aerosols type identity : * * Continental aerosols model * * * * optical condition identity : * * visibility : 50.00 km opt. thick. 550nm : 0.1518 * * * * spectral condition * * ------------------ * * etm+ 1 * * value of filter function : * * wl inf= 0.435 mic wl sup= 0.520 mic * * * * target type * * ----------- * * homogeneous ground * * constant reflectance over the spectra 0.000 * * * * target elevation description * * ---------------------------- * * ground pressure [mb] 944.86 * * ground altitude [km] 0.600 * * gaseous content at target level: * * uh2o= 2.189 g/cm2 uo3= 0.317 cm-atm * * * * atmospheric correction activated * * -------------------------------- * 0% ... unfortunately the sun angle differs from the r.sunmask output. What's wrong? > When I > use a DEM in ialt, the continuous version or the categorized, of the region, > I just get "wavelength less than 0.25 micron let's take > s(1)=s(0.25)". I don't insert an altitude value in my icdn file however, > since I've read that that value would overwrite the DEM. When I do put in an > altitude value, I get a list with the parameters for the 6S-algorithm, and > then 'percent complete', so that seems to be ok, but the algorithm stops > running, so I don't get a corrected image. Does anyone have experience with > this module, and help me with some tips, preferably so I can use my DEM > instead of one altitude value for the whole image? I have just tried on a tiny subset of lsat7_2002_10_atcorr but I see that the module uses the *entire* image: GRASS 6.5.svn (nc_spm_07):~ > g.region -p projection: 99 (Lambert Conformal Conic) ... rows: 18 cols: 26 cells: 468 GRASS 6.5.svn (nc_spm_07):~ > fg i.atcorr lsat7_2002_10 ialt=elevation icnd=icnd.txt oimg=lsat7_2002_10_atcorr D0/0: Computed r0, c289 D0/0: Computed r0, c290 D0/0: Computed r0, c291 <- running out of current region! So some work is still needed. Markus _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
