DNB Terrain Correction Performance

Steve Miller23 May 2014

Approach• Examine anthropogenic lights (cities) near sea-level and at higher

altitude.• Select two adjacent orbits passes which provide i) an eastern view,

ii) a western view.• To maximize possible parallax displacements, select locations near

scan edge.• Cloud-free views to minimize ambiguity due to obscuration and

additional parallax effects.• Compare east/west passes at each location for the original (non-

terrain-corrected) and new (terrain-corrected) geolocation data.• A consistent terrain correction will result in minimal feature shift

between the eastern and western views.

[Note: please run this powerpoint in slide-show mode in order to toggle imagery and compare the east/west views]

Selected Domain of Analysis

Baku, Azerbaijan (40.4N,49.9E,-28m)

Isfahan, Iran (32.63N,51.65E, 1.59 km)

East and West Suomi NPP Passes

East

ern

Scan

Edg

e

Wes

tern

Sca

n Ed

ge2143 UTC 2324 UTC

Baku

Isfahan

This pairing provides a nearly optimal comparison between a low and high altitude light source at opposite viewing directions…

Baku (40.4˚N, 49.9˚E,-0.28 km)

2143 UTC2324 UTC

No Correction Terrain Correction

Baku is close to sea level: parallax displacement effects are minimal Terrain correction has little impact Some notable shifts to lights West/Northwest are evident of Baku, from

higher elevation towns nestled in the Greater Caucasus Range

Isfahan (32.63˚N, 51.65˚E, 1.59 km)

At 5,217 feet (1.59 km) Isfahan parallax effects are substantial Terrain correction has significant impact (note dramatic shift of Isfahan in

the left-panel, in contrast to relative stability in the right panel.Note of caution: clouds under-lit by cities will cause apparent shifts in city light locations, since the terrain correction is done with respect to the terrain elevation, not with respect to the cloud altitudes!!!

No Correction Terrain Correction

2143 UTC2324 UTC

Summary• The ~sea level site exhibits little shift for both terrain-corrected

and non terrain-corrected geolocation, as expected. • The high-elevation site shows dramatic improvements in stability

of signal for the terrain-corrected geolocation.• Other examples (W. Straka, CIMSS) have shown the intra-band

consistency of terrain-corrected geolocation by comparing DNB with M10 and M13 imagery of fires.

• There is some evidence of changes in lights between the two passes, particularly for point sources—it has yet to be determined whether these changes are the result of lights physically changing (turn-on/off), artifacts of image registration, or (more likely) a combination of both.

• Preliminary results are encouraging—should allow for improved multi-spectral applications involving the DNB, particularly with respect to surface lights at-elevation.