topic calculation and mapping Albedo in Spatial Data Science Questions

calculation and mapping Albedo

BaffourAwuah — Tue, 08 Sep 2015 13:58:06 GMT

Can anybody here gives me some suggestions as to the best way to calculate and map Albedo effect. Those of you don't know what it is, Albedo specifies the percentage of incoming solar radiation on a surface that reflects back. I need help. Thanks, folks.

Re: calculation and mapping Albedo

DanPatterson_Retired — Tue, 08 Sep 2015 14:04:55 GMT

Albedo is determined from measurement...as per you definition... and it can be used with respect to particular wavelengths or wave bands.. Generic values can be obtained from climatology texts etc.

Is your desire to ascribe albedo values to land surfaces?
are you referring to shortwave (within visible range) or longwave/infrared albedo?
are you interested in albedo at particular wavelengths?
what type of surfaces are you interested in?
do you just want average albedo or are you interested in values that may vary by time of day or surface roughness?

Just some thoughts.

Re: calculation and mapping Albedo

BaffourAwuah — Wed, 09 Sep 2015 06:53:06 GMT

Thanks Dan. Yes my desire is to ascribe albedo values to mountain surface where there are snow stability in most part of the year making sunlight reflection possibly high. I was thinking in generic terms to find out the part of the mountain that faces the sun most. I hope you get my point.

Re: calculation and mapping Albedo

DanPatterson_Retired — Wed, 09 Sep 2015 09:02:11 GMT

Then you need the Aspect tool in the Spatial Analyst or 3D analyst extension or aspect function

http://desktop.arcgis.com/en/desktop/latest/tools/spatial-analyst-toolbox/aspect.htm

http://desktop.arcgis.com/en/desktop/latest/manage-data/raster-and-images/aspect-function.htm

You should also have a look at...

http://desktop.arcgis.com/en/desktop/latest/tools/spatial-analyst-toolbox/an-overview-of-the-solar-radiation-tools.htm

Re: calculation and mapping Albedo

BaffourAwuah — Wed, 09 Sep 2015 11:00:32 GMT

I really apreciate your suggestions. Both aproaches seem so interesting. For now I don't have the extention tool for Spatial Analysyst or 3 D analyst and the Radiation tool analyst but I have requested for one. Please do you think only the historical mountainous snow raster data and their associate statistics are enough?

Re: calculation and mapping Albedo

DanPatterson_Retired — Wed, 09 Sep 2015 12:48:53 GMT

If that is what you have, it is definitely a starting part, particularly if you can show that the historical data is consistent.

Re: calculation and mapping Albedo

BaffourAwuah — Fri, 23 Oct 2015 09:37:34 GMT

Hi again, Dan,

Sorry for the nagging. Still on my Albedo stuff. I now have my Solar Radiation calculated, Aspect
image, and Snow dataset. Please any suggestion as to the way forward?

Re: calculation and mapping Albedo

DanPatterson_Retired — Fri, 23 Oct 2015 09:43:20 GMT

You will have to come up with your classification scheme since aspect are floating point numbers. You can use the reclassify tool amongst others and class the slopes and aspects to appropriate classes along with your snow dataset (ie deep, shallow etc) and use the combine tool to delineat areas that meet certain criteria (ie N facing shallow slopes have the deepest snow...or whatever you are interested in)

Re: calculation and mapping Albedo

BaffourAwuah — Thu, 05 Nov 2015 11:47:28 GMT

Hi again, Dan.

The Reclassification and the Combine tool is working well and giving me some
interesting tables. The only problem is that I'm trying to make sense of the
values from different combination and tables to get some Albedo values. I am
attaching a sample of the combination of Snowdata and Radiation for some
suggestions.

Re: calculation and mapping Albedo

DanPatterson_Retired — Thu, 05 Nov 2015 14:05:38 GMT

the first class (value 1) ... there are 543 cells that are the combination of snowdtptrec and mradiationrec (whatever those) represent. etc etc

some times it is better to make a table out of them like a pivot table

snow typ class

rad cla 1 2 3 4 5

2 8 (your last class)

4 543 (your first)

fill in the matrix

Re: calculation and mapping Albedo

BaffourAwuah — Thu, 05 Nov 2015 14:29:47 GMT

Sure, Dan, I think I can then say that, the Albedo level is low in those cells, in the sense that the snow Level (Snowdpypt Rec) is low (1) despite the fact that the Radiation (MRadiation= 4) Level is on the high side; Am I correct?

Re: calculation and mapping Albedo

DanPatterson_Retired — Thu, 05 Nov 2015 14:33:00 GMT

Given a tabular form in the results that I have shown. You now have data that could be used in a Chi Squared test to see if there is an association/difference between the two variables...that is what cross-tabulated statistics can be used for... stretching the idea that cell counts are treated as counts and not area

Re: calculation and mapping Albedo

BaffourAwuah — Fri, 06 Nov 2015 09:37:41 GMT

Great! THE CHI-SQUARE STATISTIC IS 9442.9004. THE P-VALUE IS < 0.00001. THE RESULTS IS
SIGNIFICANT AT P< .05.