The 500 meter MODIS Level-1B data set contains calibrated and geolocated at-aperture radiances for 7 discrete bands located in the 0.45 to 2.20 µm region of the electromagnetic spectrum. These data are generated from the MODIS Level-1A scans of raw radiance and in the process are converted to geophysical units of W/(m2 µm sr). In addition, the Bidirectional Reflectance Distribution Function (BRDF) may be determined for these solar reflective bands through knowledge of the solar irradiance (e.g., determined from MODIS solar diffuser data, and from the target illumination geometry). Additional data are provided including quality flags, error estimates and calibration data.
Visible, shortwave infrared, and near infrared measurements are only made during the daytime, while radiances for the thermal infrared region (bands 20-25, 27-36) are measured continuously.
The resolution of channels 1 and 2 are 250 m, channels 3 through 7 are 500 m resolution. However, for the MODIS L1B 500 m product, the 250 m band radiance data and their associated uncertainties have been aggregated to 500 m resolution. Thus, the entire channel data set has been co-registered to the same spatial scale in the 500 m product. Separate L1B products are available for the 250 m resolution channels (MOD02QKM) and 1 km resolution channels (MOD021KM). For the latter product, the 250 m and 500 m channel data (bands 1 through 7) have been aggregated into equivalent 1 km pixel values.
Spatial resolution for pixels at nadir is 500 m, degrading to 2.4 km in the along-scan direction at the scan extremes. However, thanks to the overlapping of consecutive swaths and respective pixels there, the resulting resolution at the scan extremes is about 1 km. A 55 degree scanning pattern at the EOS orbit of 705 km results in a 2330 km orbital swath width and provides global coverage every one to two days. A single MODIS Level-1B 500 m granule will contain a scene built from 203 scans sampled 2708 times in the cross-track direction, corresponding to approximately 5 minutes worth of data; thus 288 granules will be produced per day. Since an individual MODIS scan will contain 20 along-track spatial elements for the 500 m channels, the scene will be composed of 2708 by 4060 pixels, resulting in a spatial coverage of 2330 km by 2040 km. Due to the MODIS scan geometry, there will be increasing scan overlap beyond about 20 degrees scan angle.