Ok, I have done a bit more digging and found r.univar for the stats problem -
don't know how I missed that one!
On the atmospheric correction I have ditched i.landsat.dehaze in favour of the
presumed higher accuracy of i.atcorr. So, with this I have created a control
file with the relevant values for e.g. Band-3:
#--------- start of control file -----
8 - geometrical conditions=Landsat ETM+
3 24 08.020 35.400 32.680 - month day hh.ddd longitude latitude ("hh.ddd" is
in GMT decimal hours)
2 - atmospheric mode=midlatitude summer
2 - aerosols model=maritime
50 - visibility [km] (aerosol model concentration)
-0.080 - mean target elevation above sea level [km]
-1000 - sensor on board a satellite
63 - 3rd band of ETM+ Landsat 7
#--------- end of control file -------
When I then run i.atcorr:
$ i.atcorr -r -a iimg=R3 icnd=icnd3.txt oimg=C3D
ERROR: Raster map <dem_float> not found
The error is refers to the default altitude raster-map, but the command help
specifies that the ialt argument is optional and I don't have a DEM for the
area. Any ideas what is going on?
Thanks,
Jamie
________________________________
From: James Travers <[email protected]>
To: "[email protected]" <[email protected]>
Sent: Wednesday, 2 May 2012, 22:10:39
Subject: [GRASS-user] Negative raster values from i.landsat.dehaze
Hi,
I have been trying to get some results from GRASS for a couple of weeks now but
am hitting a wall. What I am trying to do is to take an area of land from a
series of Landsat 7 ETM+ images and calculate NDVI over the area for the
purpose of comparison over a time-period. This obviously requires atmospheric
correction, so the command sequence I am using after importing the images for a
given mapset is:
# Generate radiance values
i.landsat.toar input_prefix="B" output_prefix="R"
metfile="./L71174038_03820080324/L71174038_03820080324_MTL.txt" sensor="tm7"
# Atmospheric correction
i.tasscap -7 band1=R1 band2=R2 band3=R3 band4=R4 band5=R5 band7=R7 outprefix=TC
i.landsat.dehaze band1=R1 band2=R2 band3=R3 band4=R4 band5=R5 band7=R7
tasscap4=TC.4 outprefix=D
# Generate NDVI map
r.mapcalc 'ndvi=if((D.3 == 0 && D.4 == 0), -1, (D.4 - D.3) / (D.4 + D.3))'
Then I mask the NDVI map with an area raster which I already created. There is
probably a better way of doing this.
# Mask NDVI map with individual regions
r.mapcalc 'area_ndvi = ndvi * area_mask@PERMANENT'
Finally I want an average value of the NDVI over the area. There is definitely
a better way of doing this but I couldn't find a grass command that spits out a
single value. Instead I used r.stats to give the area of each group of values
and then wrote a Perl script to average these.
# Process statistics
r.stats -a --q area_ndvi | ./stats.pl
Ok, so here come the questions:
1) Is there a better way to simply get an average of all values over a given
area to replace my stats.pl script?
2) and this is the big one. When I perform i.landsat.dehaze I get rasters with
primarily negative values. This renders the NDVI calculation meaningless as
they are ratios of +ve and -ve values. I am presuming this is a mistake as
negative reflectance has little meaning anyway - did I use the wrong sequence
of commands? Below are info outputs for the red-band after the TOAR and dehaze
operations respectively:
Many thanks for any help on this,
Jamie
+----------------------------------------------------------------------------+
| Layer: R3 Date: Wed May 2 20:15:30 2012 |
|
Mapset: L71174038_03820080324 Login of Creator: jamie |
| Location: area |
| DataBase: /home/jamie/grassdata |
| Title: ( R3
) |
| Timestamp: none
|
|----------------------------------------------------------------------------|
| |
| Type of Map: raster Number of Categories: 255 |
| Data Type:
DCELL |
| Rows: 6961 |
| Columns:
7911 |
| Total Cells: 55068471 |
| Projection: UTM (zone
36) |
| N: 3619200 S: 3410370 Res: 30 |
| E: 843630 W: 606300 Res: 30 |
| Range of data: min =
-0.0129146013370688 max = 0.605436510681785 |
| |
| Data Description: |
| generated by
i.landsat.toar |
| |
|
Comments: |
| Reflectance of Landsat-7 ETM+ (method uncorrected) |
| ---------------------------------------------------------------- |
| Acquisition date ...................... 2008-03-24
|
| Production date ....................... 2012-02-23 |
| |
| Earth-sun distance (d) ................ 0.99699779 |
| Digital number (DN) range ............. 1 to
255 |
| Calibration constants (Lmin to Lmax) .. -5.000 to +234.400 |
| DN to Radiance (gain and bias) ........ +0.94252 and -5.94252 |
| Mean solar irradiance (ESUN) .......... 1551.000 |
| Reflectance = Radiance divided by ..... 387.15868 |
|
----------------------------------------------------------------- |
| |
| i.landsat.toar input_prefix="B" output_prefix="R" metfile="./L711740\ |
| 38_03820080324/L71174038_03820080324_MTL.txt" sensor="tm7" method="u\ |
| ncorrected" percent=0.01 pixel=1000 sat_zenith=8.2000 rayleigh=0.0
|
| |
+----------------------------------------------------------------------------+
+----------------------------------------------------------------------------+
| Layer: D.3 Date: Wed May 2 20:22:21 2012 |
| Mapset:
L71174038_03820080324 Login of Creator: jamie |
| Location: area |
| DataBase: /home/jamie/grassdata |
| Title: ( D.3
) |
| Timestamp: none
|
|----------------------------------------------------------------------------|
| |
| Type of Map: raster Number of Categories: 255 |
| Data Type:
DCELL |
| Rows: 334 |
| Columns:
166 |
| Total Cells: 55444 |
| Projection: UTM (zone
36) |
| N: 3493000 S: 3483000 Res: 29.94011976 |
| E: 649000 W: 644000 Res: 30.12048193 |
| Range of data: min = -0.463376848126162 max = 0.19725822381175
|
| |
| Data Description: |
| generated by
r.mapcalc |
| |
|
Comments: |
| R3 - (TC.4 - 0.134975) * -3.08586
|
| |
+----------------------------------------------------------------------------+
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