The draft journal article “Current GISS Global Surface Temperature Analysis” posted at http://data.giss.nasa.gov/gistemp/paper/gistemp2010_draft0319.pdf provides a link to the nightlight radiance data set [Imhoff et al., 1997] used [http://www.ngdc.noaa.gov/dmsp/download_rad_cal_96-97.html] (measurements made between March 1996 and February 1997)] at a resolution of 30″ x 30″.
While I was unable to simultaneously view the terrain detail and the NASA nightlight layer which comes with Google Earth, the nightlight radiance data from the TIFF files in this data set can be added to the Google Earth tours described in my earlier post.
The image below shows my “home station” with the radiance values added in green. I have also added a yellow rectangle centred on the station and extending 0.005 degrees N/S and E/W, showing the locations which when rounded to 0.01 degrees will give this pushpin location. The radiance index in v2.inv (33) matches the radiance value closest to the station pushpin (as did the radiance values for the other Irish stations).
For comparison, here is the same station, but using radiance values from the lower resolution TIFF image downloaded.
[ Code to follow. I suspect the radiance values may be slightly shifted north-west, as the file description for the radiance seems to suggest such a shift (although it is also possible that I have introduced this slight shift myself!). For now this is a “draft” post which will be corrected or expanded later. ]
[ Expansion March 27th 2010 ]
The question of a possible shift arises as the dimensions of the downloaded 96-97 TIFF file are 43200 pixels by 21600 pixels, one short of the number required to give complete 360 degree by 180 degree coverage at 30″ by 30″ (for comparison the version 4 DMSP-OLS TIFF files are 43201 pixels wide by 16801 pixels deep [latitude coverage from -65 to 70 degrees only]). If it is assumed that the actual grid size is slightly increased from 30″ by 30″ to give full coverage, the shift involved can be seen by comparing the yellow and green figures in the two illustrations below: for Dublin Airport
and Saipan (a greater shift for a southern hemisphere location, further towards 180 East)
(I will try to get this point clarified by NGDC)
I am disappointed in the degree of accuracy/precision between GISS and myself in the parsing of DMSP/RC data. While there is a visible rough correlation, I expected better.
This seems largely a question of the rounding/truncation habits of the Gistemp group (when porting Gistemp with added output information I found that the only way to achieve a perfect match to the original Gistemp output was by means of extensive special-case rounding tables, to take care of the many instances of rounding of values close to 0.5 in unexpected directions). In this case, rounding the image row calculated from latitude to the nearest row gave 1230 differences from the GISS values, whereas truncation to the next row to the north (TIFF images are stored top down) reduced this to 121 differences.
Without the GISS code to examine it is hardly worth spending more time trying to reconcile the remaining differences, particularly as it is also entirely possible that the GISS draft paper may be incorrect in citing the 96-97 data, which is the data set currently archived. Reading the cited Imhoff et al.  might suggest that earlier data may have been used, which is no longer available for download.
The GISS draft paper also states:
For these reasons, beginning in January 2010 the standard GISS analysis employs global
nightlights in choosing stations to be adjusted for urban effects. Use of nightlights is a well-
defined objective approach for urban adjustment, and the nightlight data set used for the
adjustment is readily available (see http address above).
The standard nightlight adjustment defines rural as nightlight radiance less than 32
From which you might conclude that this standard nightlight adjustment has been employed in the standard GISS analysis since January 2010, but examination of the archived log files shows that in fact the rural definition of less than 11 which was used in the October 2009 test is still being used. Has anyone at GISS noticed? In this regard some might also consider the shifting balance between rural and urban stations a rather large elephant lurking in the room which deserves mention in the draft paper: from 2507 rural/3795 urban prior to the global application of the nightlight criterion, via 3123 rural/3179 urban for the criterion actually now applied, to 5334 rural/968 urban for the standard adjustment described in the draft paper. A minor change not worth mentioning? Possibly not of course if you also believe you have stations located with a resolution of 0.01 degrees of latitude and longitude because that is the number of digits appearing in the file.
Correction (April 14, 2010): in fact the Gistemp group have in fact followed their draft article. I missed a conversion equation relating DN values (used in the night lights TIFF file and in v2.inv) to the radiance values referred to in the draft article. The number of additional rural stations, just over 600, is still substantial, although not as extreme a change as I earlier thought.
[ code to follow when rewritten in R. At present this is still a C# console application ]