Re: [GRASS-user] Creating turbidity raster file
Markus Neteler wrote: You have to use the zcolumn parameter to indicate which column to use. Hope this helps, Markus It worked!! thanks a lot -- View this message in context: http://n2.nabble.com/Creating-turbidity-raster-file-tp2297732p2301479.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Creating turbidity raster file
Dylan Beaudette wrote:
On Monday 09 February 2009, Hamish wrote:
buraq wrote:
I have formatted csv files for every month which is like
latitude;longitude;turbidityValue. So I want to create
raster files from these csvs for using in r.sun.
v.in.ascii - convert .csv to a vector points file
g.region # set up raster grid
v.surf.rast - interpolate vector points to raster surface
Minor correction:
v.surf.rast --- v.surf.rst
I have worried about r.sun's Linke Turbidity factor values in areas with
big changes in elevation. Is turbidity value heavily dependent on
altitude?
It should, as it is based on a measure of optical thickness (air mass):
Extracted from a document --
m = \frac{1}{sin(\alpha) + 0.15(\alpha + 3.885)^{-1.253}} e^{-0.0001184
\times
A}
\noindent
where $\alpha$ is the solar elevation angle at (12:00 pm local time) on
each
day of the year, and $A$ is the weather station elevation in meters above
mean sea level (MSL).
Extracted from a document --
This stuff is also on pages 40-41 of this document:
http://169.237.35.250/~dylan/d_e_beaudette-ms_thesis.pdf
Cheers,
Dylan
Hamish
--
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341
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I took the turbidity values from soda-is.com. I entered no altitude value
for the latitude and longitude.
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Re: [GRASS-user] Creating turbidity raster file
Hamish:
I have worried about r.sun's Linke Turbidity factor values in areas with
big changes in elevation. Is turbidity value heavily dependent on
altitude?
Jose:
Linke turbidity is certainly height-dependent given the higher optical
path length at lower elevations. A simple approximated pressure correction
might be applied if the turbidity at a given altitude z' is known:
TL(z) = TL(z') exp( -(z-z') / 8435.2)
Dylan:
It should, as it is based on a measure of optical thickness (air mass):
m = \frac{1}{sin(\alpha) + 0.15(\alpha + 3.885)^{-1.253}} e^{-0.0001184
\timesA}
(yay LyX, ctrl-m, paste selection, view PostScript)
buraq wrote:
I took the turbidity values from soda-is.com. I entered no altitude
value for the latitude and longitude.
I did the same, I attempted to match their model grid (approx 1x1-deg IIRC)
for an array of lat/lon extractions over my study area, then v.surf.rst to
produce a Linke layer for r.sun. I can't recall off the top of my head if
we entered an altitude or not, I think not.
I work in fjords with 1000m vertical drops (including one of the top
10 tallest waterfalls in the world). With little idea of the elevation
values used for the SODA data, I just guess that it will be very rough
and subject to a somewhat arbitrary sampling error.
I assume I'll have to use one of the above formulas with r.mapcalc to
create the Linke layer from the SODA data a local DEM for delta-z. But
that just makes me wonder if turbidity really belongs in a 3D voxel grid,
not a 2D coverage map? i.e. I can derive a value for Linke at the
ground-surface for each raster cell in the DEM easily enough using the
above formulas, but isn't the important Linke value(s) what the beam
encounters on it's path through the atmosphere high above the ground,
not just the value at ground level at the beam's terminus?
If it helps, I do have quite a bit of PAR light meter data we collected
at sea level throughout the region over full years; and do know the air
is nearly as clear as it gets. What instrumentation could I add to our
met stations to get a better record? Deploying light loggers on mountain
peaks for the summer months may be an option (granite is beautiful stuff
to climb :).
hope that makes sense,
Hamish
ps- If anyone is interested, at one point I wrote a little C program
that fit a sine curve to the monthly data and gave you a per-day value
from per-month data, avoiding big jumps at the month changes. The same
could in theory be adapted to work with r.mapcalc to get daily maps from
the monthly raster layers, at considerable computational cost. (but you
just need to run it once(ie x365) in a dedicated mapset)
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[GRASS-user] Creating turbidity raster file
Hi all, I am new in grass. Maybe that can be easy for you.. I have formatted csv files for every month which is like latitude;longitude;turbidityValue. So I want to create raster files from these csvs for using in r.sun. What I have done so far, I created MIFs in mapInfo then imported grass using v.in.ogr. Then I used v.surf.rst to make them raster. But I think it's failed. I got that http://n2.nabble.com/file/n2297732/MapDisplay.png MapDisplay.png How can I do this right? Thanks for your help -- View this message in context: http://n2.nabble.com/Creating-turbidity-raster-file-tp2297732p2297732.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Creating turbidity raster file
On Mon, Feb 9, 2009 at 4:27 PM, buraq zak...@gmail.com wrote: Hi all, I am new in grass. Maybe that can be easy for you.. I have formatted csv files for every month which is like latitude;longitude;turbidityValue. So I want to create raster files from these csvs for using in r.sun. What I have done so far, I created MIFs in mapInfo then imported grass using v.in.ogr. Then I used v.surf.rst to make them raster. But I think it's failed. I got that http://n2.nabble.com/file/n2297732/MapDisplay.png MapDisplay.png How can I do this right? You have to use the zcolumn parameter to indicate which column to use. Hope this helps, Markus ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Creating turbidity raster file
buraq wrote: I have formatted csv files for every month which is like latitude;longitude;turbidityValue. So I want to create raster files from these csvs for using in r.sun. v.in.ascii - convert .csv to a vector points file g.region # set up raster grid v.surf.rast - interpolate vector points to raster surface I have worried about r.sun's Linke Turbidity factor values in areas with big changes in elevation. Is turbidity value heavily dependent on altitude? Hamish ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Creating turbidity raster file
buraq wrote: I have formatted csv files for every month which is like latitude;longitude;turbidityValue. So I want to create raster files from these csvs for using in r.sun. v.in.ascii - convert .csv to a vector points file g.region # set up raster grid v.surf.rast - interpolate vector points to raster surface I have worried about r.sun's Linke Turbidity factor values in areas with big changes in elevation. Is turbidity value heavily dependent on altitude? Linke turbidity is certainly height-dependent given the higher optical path length at lower elevations. A simple approximated pressure correction might be applied if the turbidity at a given altitude z' is known: TL(z)=TL(z')exp(-(z-z')/8435.2) with z and z' given in meters. This could be easily applied using r.mapcalc Jose Hamish ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user -- José A. Ruiz-Arias Solar Radiation and Atmosphere Modelling Group http://www.ujaen.es/investiga/tep220 Physics Department, University of Jaén Campus Lagunillas, Building A3 066 23071 Jaén Spain Tlf: +34 953 212 474 Fax: +34 953 212 838 ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Creating turbidity raster file
On Monday 09 February 2009, Hamish wrote:
buraq wrote:
I have formatted csv files for every month which is like
latitude;longitude;turbidityValue. So I want to create
raster files from these csvs for using in r.sun.
v.in.ascii - convert .csv to a vector points file
g.region # set up raster grid
v.surf.rast - interpolate vector points to raster surface
Minor correction:
v.surf.rast --- v.surf.rst
I have worried about r.sun's Linke Turbidity factor values in areas with
big changes in elevation. Is turbidity value heavily dependent on altitude?
It should, as it is based on a measure of optical thickness (air mass):
Extracted from a document --
m = \frac{1}{sin(\alpha) + 0.15(\alpha + 3.885)^{-1.253}} e^{-0.0001184 \times
A}
\noindent
where $\alpha$ is the solar elevation angle at (12:00 pm local time) on each
day of the year, and $A$ is the weather station elevation in meters above
mean sea level (MSL).
Extracted from a document --
This stuff is also on pages 40-41 of this document:
http://169.237.35.250/~dylan/d_e_beaudette-ms_thesis.pdf
Cheers,
Dylan
Hamish
--
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341
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