Recall that reflectance is a measure of the ratio between the observed (outgoing)
radiation from a surface and the expected incoming radiation incident on that
surface
– reflectance is typically a value between 0 and 1
• Since the DNB operates day and night, there are two sources of expected
radiation: the sun and moon
– Converting DNB radiance to NCC reflectance involves accurate modeling of both solar
radiation and lunar radiation
• However, the DNB also detects radiation from other sources (lightning, auroras,
city lights, fires, etc.) which can be several orders of magnitude brighter than the
solar and/or lunar radiation (particularly at night during a new moon) and these
light sources cannot be modeled
– NCC reflectance values were originally allowed to vary between 0 and 5, but they may
approach 100-1000 or more in cases of auroras, city lights and fires, for example
– As a result, NCC processing typically produced large areas of “SOUB” fill values indicating
values out-of-bounds for nighttime granules when the moon was significantly less than full
– A fix for this issue is now operational so that NCC imagery is valid during all phases of the
moon as it is supposed to be (fix implemented on 10 July 2013)