topic Re: Raster: Converting digital numbers to real world values in ArcGIS Spatial Analyst Questions

Raster: Converting digital numbers to real world values

LamaZip — Sun, 12 Dec 2021 16:23:42 GMT

I have downloaded 2 chlorophyll maps which generally have cell values of 0-255.

How can I convert these into real world values?

Following the instructions linked here and here, I have been unable to convert the byte value (0-255) to geophysical values (0-64 mg m3)

Details

I have downloaded L3 choloprhyll data maps. I have extracted and attempted to convert the cell values in R, with no luck.

Is this possible in Arcmap and how would it be achieved?

# DN = digital number / cell value / cholorphyll L3 data
# value = 10^^{[(DN * slope) + intercept]
# raster = Modis cholorphyll sattelite image 

# Code ran in R}
((values(raster)* 0.015) -2.0)^10)
# Does not return real world values (values between 0-64 mg m-3)

Linked below is one of the raster images I have attempted to convert into real world geophyiscal values, which was downloaded from Giovanni (after clicking the link, click plot, select an image and download as a TIFF. Attachment limits prevent me from directly uploading image. OR just download image attachment in comment below)

Question:

How can I convert the pixel values (0-255) of a cholorphyll L3 TIFF image into real word values, using Arcmap?

Re: Raster: Converting digital numbers to real world values

LamaZip — Tue, 30 Aug 2016 11:39:36 GMT

Click image attachment to download TIFF of CHL map.

Re: Raster: Converting digital numbers to real world values

DanPatterson_Retired — Tue, 30 Aug 2016 11:43:08 GMT

python field calculator power x ** y 10**((DN*slope) + intercept)

raster power tool Power—Help | ArcGIS for Desktop

raster calculator **—Spatial Analyst module | ArcGIS for Desktop

Re: Raster: Converting digital numbers to real world values

LamaZip — Tue, 30 Aug 2016 12:30:40 GMT

Sorry I'm a little confused. Could you provide an explanation with your comment? Thanks

Re: Raster: Converting digital numbers to real world values

DanPatterson_Retired — Tue, 30 Aug 2016 12:55:13 GMT

I was showing how to implement your equation in either the field calculator, in the spatial analyst , power is implemented in 2 ways.

So what is the question then? Are you trying to figure out how to implement the equation? is so, I provided how to get power (ie ** or Power) You seem to have a DN raster (?) but what about slope and intercept?