How to intepret slope on Temperatures rasters

[Alejandro Hinojosa Corona]

Hello grass colleagues:

I am applying the slope formula proposed by Shapiro and Westervelt in the
"R.MAPCALC An Algebra for GIS and Image Processing" document to
a raster map of Sea surface temperatures.
The raster is in lat-long with a cell size of 5 minutes in both latitude
and longitud. The raster values are temperatures coded as 10ths of a degree
Celsius.

 The formula applied is:

slope = eval( \
              x= (DTM[-1,-1] + 2 * DTM[0,-1] + DTM[1,-1]          \
                 -DTM[-1,1]  - 2 * DTM[0,1]  - DTM[1,1])/8.0,    \                       
              y= (DTM[-1,-1] + 2 * DTM[-1,0] + DTM[-1,1]    \
                 -DTM[1,-1] -  2 * DTM[1,0]  - DTM[1,1])/ (8.0 ), \
             atan(sqrt(x * x + y *y)))    
 
The output  is a slope raster with values in degrees
ranging from  0 to 90.
My question is:
     -how to interpret raster output as change in temperature per cell.
     -how to transform the slope value in degrees to an increment in temperature
      per unit cell.

 Best Regards

Alejandro Hinojosa    
alhinc at cicese.mx    http://www.cicese.mx/~alhinc
Research Associate
Earth Sciences Division
CICESE 
Ensenada, Baja California, Mexico.