Abstract:
The MODIS Level 1B data set contains calibrated and geolocated at-aperture radiances for 36 discrete bands located in the 0.4 to 14.4 micron region of electromagentic 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 the solar reflective bands (1-19, 26) 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.
Channels 1 and 2 have 250 m resolution, channels 3 through 7 have 500 m resolution, and the rest have 1 km resolution. However, for the MODIS L1B 1 km product, the 250 m and 500 m band radiance data and their associated uncertainties have been aggregated to 1 km resolution. Thus the entire channel data set is referenced to the same spatial and geolocation scales. Separate L1B products are available for the 250 m channels (MOD02QKM) and 500 m channels (MOD02HKM) that preserve the original resolution of the data.
Spatial resolution for pixels at nadir is 1 km, degrading to 4.8 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 2 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 granule will nominally contain a scene built from 203 scans (or swaths) sampled 1354 times in the cross-track direction, corresponding to approximately 5 minutes worth of data. Since an individual MODIS scan (or swath) will contain 10 along-track spatial elements, the scene will be composed of (1354 x 2030) pixels, resulting in a spatial coverage of (2330 km x 2030 km).Due to the MODIS scan geometry, there will be increasing overlap occurring beyond about 25 degrees scan angle.
To summarize, the MODIS L1B 1 km data product consists of:
1. Calibrated radiances and uncertainties for (2) 250 m reflected solar bands aggregated to 1 km resolution
2. Calibrated radiances and uncertainties for (5) 500 m reflected solar bands aggregated to 1 km resolution
3. Calibrated radiances and uncertainties for (13) 1 km reflected solar bands and (16) infrared emissive bands
4. Geolocation subsampled at every 5th pixel across and along track
5. Satellite and solar angles subsampled at the above frequency
6. 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 the full-resolution geolocation and solar/satellite geometry can obtain the separate MODIS Level 1 Geolocation product (MOD03) from LAADS.
The MODIS L1B 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 260 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 MOD021KM)
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.
An incorrect comparison between RVS coefficients for Thermal Emissivity Bands (TEB) and Reflective Solar Bands (RSB) was being made during the calculation of the RVS coefficients. This was replaced with a comparison between TEB coefficients. This error never resulted in an incorrect RVS correction but did lead to re-calculating the coefficients for each detector in a thermal band even if the coefficients were the same for all 10 detectors.
A destriping algorithm for Band 26 devised by C. Moeller was implemented. A new time-dependent LUT was added which gives coefficients for a detector-specific cross-talk correction based on the aggregated Band 5 radiances. The Band 26 scaled integers are adjusted by the Band 5 correction term, which is the product of the Band 5 radiance times the ratio of the Band 5 to Band 26 scaling factors times the LUT correction value for that detector. In addition a new LUT which allows for a frame offset with regard to the Band 5 radiance was added. A LUT which switches the correction off or on was also added.
Description:
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.
Latitude Resolution:
1 km at nadir
Longitude Resolution:
1 km at nadir
Horizontal Resolution Range:
1 km - < 10 km or approximately .01 degree - < .09 degree
Temporal Resolution:
Two day repeat observations with a repeat orbit pattern every 16 days.
Temporal Resolution Range:
Daily - < Weekly
