The MODVOLC files
Each time you produce a hot-spot map, for any geographic area and any time period, the MODVOLC data used to produce it are available via a hyperlink. MODVOLC files are space-delimited ASCII text files containing 22 fields of data.
||UNIX time that the hot-spot was observed. The number of seconds since 00:00:00 in UCT on January 1, 1970
||The MODIS sensor that detected the hot-spot. T = Terra-MODIS; A = Aqua-MODIS.
|Fields 3 to 7:
||Time that the hot-spot was observed. Respectively, the year/month/day/hour/minute in UCT.
|Fields 8 and 9:
||Respectively, the geodetic longitude and latitude of the centre-point of the hot-spot pixel, referenced to the WGS-84 ellipsoid.
|Fields 10 to 14:
||Spectral radiance, in W m-2
sr-1 μm-1, detected from the hot-spot pixel
in MODIS bands 21, 22, 6, 31, and 32, respectively, with central
wavelengths of 3.959 μm, 3.959 μm, 1.64 μm, 11.03 μm,
and 12.02 μm. Bands 21 and 22 both cover the same spectral
interval but have different dynamic ranges; band 22 is sensitive to
whole pixel temperatures of up to ∼330 K, band 21, ∼500 K.
The band 22 detectors often saturate over highly radiant surfaces.
Saturation in band 22 (or indeed any of the bands) is flagged by a
fill value of -10.000. During the night, when the reflective
channels are turned off, field 12 reports a fill value of ∼170. Although we use corrected radiances in the daytime product (click here for an explanation) only the original uncorrected pixel radiances are reported in this file.
|Fields 15 to 18:
||Sun-sensor geometry at moment of hot-spot observation. Respectively, the satellite zenith, satellite azimuth, solar zenith, and solar azimuth of the hot-spot pixel, in degrees. Field 16, the solar zenith, can be used to discriminate nighttime and daytime observations (i.e. was the sun above or below the horizon).
|Fields 19 and 20:
||Location of the hot-spot pixel in image coordinates. The line and sample of the hot-spot in the original MOD021KM.* MODIS granule.
||NTI of the hot-spot pixel. By day, this value will be ≥ -0.60; by night, ≥ -0.80.
||The sun-glint angle, computed from the sun-sensor geometry data (fields 14 to 17). Pixels that are candidates for sun-glint contamination are not portrayed in the image maps you may create. However, the details of these pixels are retained in the MODVOLC data-base and files. We use a sun-glint threshold of 12°. If a pixel has a sun-glint angle of < 12° it is potentially contaminated by sunglint and should not be trusted. Obviously, sun-glint is only an issue for daytime hot-spots. Due to restrictions on the complexity of the algorithm as it runs at Goddard Space Flight Centre, we calculate this value in-house.