Abstract: 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 micron region of the electromagnetic spectrum. These data are generated from the MODIS Level 1A scans of raw radiance and in the process converted to geophysical units of W/(m^2 um sr). In addition, the Earth ... Bi-directional 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.
Channel locations for the MODIS 500 meter data are as follows:
Channels 1 and 2 have 250 m resolution, channels 3 through 7 have 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 km, degrading to 2.4 km in the along-scan direction at the scan extremes. However, thanks to the overlapping of consecutive swaths and respectively 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 x 4060) pixels, resulting in a spatial coverage of (2330 km x 2040 km). Due to the MODIS scan geometry, there will be increasing scan overlap beyond about 20 degrees scan angle.
To summarize, the MODIS L1B 500 m data product consists of:
1. Calibrated radiances, uncertainties and number of samples for (2) 250 m reflected solar bands aggregated to 500 m resolution
2. Calibrated radiances and uncertainties for (5) 500 m reflected solar bands
4. Calibration data for all channels (scale and offset)
5. Comprehensive set of file-level metadata summarizing the spatial, temporal and parameter attributes of the data, as well as auxiliary information pertaining to instrument status and data quality characterization
Users requiring all geolocation and solar/satellite geometry fields at 1km resolution can obtain the separate MODIS Level 1 Geolocation product (MOD03) from LAADS http://ladsweb.nascom.nasa.gov/ .
The MODIS L1B 500 m data are stored in the Earth Observing System Hierarchical Data Format (HDF-EOS) which is an extension of HDF as developed by the National Center for Supercomputer Applications (NCSA) at the University of Illinois. A typical file size will be approximately 170 MB.
Environmental information derived from MODIS L1B measurements will offer a comprehensive and unprecedented look at terrestrial, atmospheric, and ocean phenomenology for a wide and diverse community of users throughout the world.
(The Shortname for this product is MOD02HKM)
The V004 Program Executable (PGE), for MODIS Level 1B products, has gone through a series of revisions since the initial release of V4.0.0 in March of 2002. These include revisions to make it LINUX-compatible. The current version is V4.0.9, which does not contain changes to the code that affect scientific output.
Below is a brief overview of changes that affect scientific output in previous versions (V4.0.0 to V4.0.7) of PGE code. The MCST web site, listed in the URL section of this DIF, has a more detailed version of this information, including revisions that do not affect scientific output.
Significant changes to Look Up Tables (LUT) used in Level 1B processing have occurred. These include revising the Response-versus-Scan Angle (RVS) LUTs from listing the RVS corrections to listing the quadratic coefficients used in making the RVS correction. The coefficients are now calculated by interpolating on the granule collection time and the RVS corrections are then generated using the interpolated coefficients. Previously used Emissive and Reflective RVS LUT tables were eliminated and new ones introduced.
Near real-time (NRT) data are available from MODAPS for certain Aqua and Terra MODIS L0, L1, L2, L2G, and L3 products. Whereas the standard MODIS forward processing acquires 2-hour L0 files for Aqua and Terra from EDOS within 7-8 hours of real time, LANCE-MODIS acquires session-based L0 files from EDOS and the end of the session is available within 10-30 minutes after real time.
Horizontal Resolution Range:
500 meters - < 1 km
Two day repeat observations with a repeat orbit pattern every 16 days.
Temporal Resolution Range:
Daily - < Weekly