Folks:
I was wondering if there is a way to turn the atmosphere "off" in
r.sun, and model a top of atmosphere radiation?
--j
--
Jonathan A. Greenberg, PhD
Assistant Project Scientist
Center for Spatial Technologies and Remote Sensing (CSTARS)
Department of Land, Air and Water Resources
University of California, Davis
One Shields Avenue
Davis, CA 95616
Phone: 415-763-5476
AIM: jgrn307, MSN: jgrn307@hotmail.com, Gchat: jgrn307
On Monday, May 16, 2011, Jonathan Greenberg wrote:
Folks:
I was wondering if there is a way to turn the atmosphere "off" in
r.sun, and model a top of atmosphere radiation?--j
Hi Jonathan,
If you check out the metadata associated with the output from r.sun, you will
find the following: (note the "Extraterrestrial irradiance" entry)
r.info rad_beam.187
+----------------------------------------------------------------------------+
| Layer: rad_beam.187 Date: Thu Mar 24 17:17:43 2011
|
| Mapset: PERMANENT Login of Creator: dylan
|
| Location: ca630
|
| DataBase: /home/dylan/grass
|
| Title: ( rad_beam.187 )
|
| Timestamp: none
|
|----------------------------------------------------------------------------|
|
|
| Type of Map: raster Number of Categories: 255
|
| Data Type: FCELL
|
| Rows: 1396
|
| Columns: 553
|
| Total Cells: 771988
|
| Projection: UTM (zone 10)
|
| N: 4235950 S: 4221990 Res: 10
|
| E: 697230 W: 691700 Res: 10
|
| Range of data: min = 4492.042 max = 7758.583
|
|
|
| Data Description:
|
| generated by r.sun
|
|
|
| Comments:
|
| ----------------------------------------------------------------
|
| Day [1-365]: 187
|
| Solar constant (W/m^2): 1367
|
| Extraterrestrial irradiance (W/m^2): 1321.303439
|
| Declination (rad): 0.396193
|
| Latitude min-max(deg): 38.1250 - 38.2500
|
| Sunrise time min-max (hr.): 4.72 - 4.72
|
| Sunset time min-max (hr.): 19.28 - 19.28
|
| Time step (hr.): 0.5000
|
| Linke turbidity factor: 3.0
|
| Ground albedo: 0.200
|
| -----------------------------------------------------------------
|
|
|
| r.sun -s elevin="ned10m" aspin="aspect10m" aspect=270 slopein="slope\
|
| 10m" slope=0.0 lin=3.0 alb=0.2 beam_rad="rad_beam.187" day=187 step=\
|
| 0.5 dist=1.0 numpartitions=1
|
--
Jonathan A. Greenberg, PhD
Assistant Project Scientist
Center for Spatial Technologies and Remote Sensing (CSTARS)
Department of Land, Air and Water Resources
University of California, Davis
One Shields Avenue
Davis, CA 95616
Phone: 415-763-5476
AIM: jgrn307, MSN: jgrn307@hotmail.com, Gchat: jgrn307
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user
--
Dylan E. Beaudette
USDA-NRCS Soil Scientist
California Soil Resource Lab
http://casoilresource.lawr.ucdavis.edu/
Jonathan Greenberg wrote:
I was wondering if there is a way to turn the
atmosphere "off" in r.sun, and model a top of
atmosphere radiation?
I wonder if it enough to keep the cloud coefficients (i.e. coefbh, coefdh
r.rescale'd GRIB files) at the default clear-sky conditions, and set
the Linke coefficient at lin=1.00.
then compare how well the direct beam result matches the solar constant?
(aka the see what happens experimental approach)
Hamish
On Sunday, May 22, 2011, Hamish wrote:
Jonathan Greenberg wrote:
> I was wondering if there is a way to turn the
> atmosphere "off" in r.sun, and model a top of
> atmosphere radiation?I wonder if it enough to keep the cloud coefficients (i.e. coefbh, coefdh
r.rescale'd GRIB files) at the default clear-sky conditions, and set
the Linke coefficient at lin=1.00.then compare how well the direct beam result matches the solar constant?
(aka the see what happens experimental approach)Hamish
I would be interested in the result, and happy to test. Any tips on getting
started with the coef maps and GRIB (not sure what that is)?
Dylan
--
Dylan E. Beaudette
USDA-NRCS Soil Scientist
California Soil Resource Lab
http://casoilresource.lawr.ucdavis.edu/
Dylan wrote:
I would be interested in the result, and happy to test.
maybe testing is as easy as running the test for elevation.10m
in the spearfish dataset, or the r.volcano example from the r.sun
wiki page http://grass.osgeo.org/wiki/R.sun
with lin=1.0, and checking the value you pointed out in the
r.info metadata?
Any tips on getting started with the coef maps and GRIB
(not sure what that is)?
GRIB is "GRIdded Binary", and is the standard output raster
format for atmospheric/wave model forecast data. GDAL can read it
(although AFAIK /still/ suffers from a 1/2 cell grid registration
bug so needs a r.region correction after import)
Interfacing with that data is parthly what I wrote d.barb to work
with, although d.rast.arrow will partly do the job as well.
Other free software like zyGrib.org and OpenCPN.org can be used
to visualize it.
I've just now written up a 5 minute quickstart for using zygrib,
see the link at the end of this page:
http://adhoc.osgeo.osuosl.org/livedvd/docs/en/overview/zygrib_overview.html
zygrib does a really nice job of animating cloud cover, give it
a try!
how how to translate that to the beam and diffuse coefficients
for r.sun ... hmmm ... well I guess the beam value would be the
opacity of the cloud ceiling, and diffuse would be the opacity
of the fog.
The man page says they want to be scaled from 0.0-1.0, and
r.rescale can do that from the r.in.gdal'd GRIB data. I assume
0.0 is clear sky but I'm not sure what 1.0 would be equivalent
to.. a grim black sky as you might get under a thundercloud?
Probably just the GRIB file's cloud-cover max is highly variable
and not appropriate.
Hamish