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When utilizing the SMAP Near-Real-Time (NRT) data products (SPL2SMP_NRT and SPL1BTB_NRT) it is important to understand how they differ from standard SMAP data products and their limitations. Below we outline the main differences in each NRT data product.SPL1BTB_NRT:

The NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC) provides access to two SMAP LANCE Near Real Time data sets:

The following table describes both the required and actual latencies for the different SMAP radiometer data sets. Latency is defined as the time (# days, hh:mm:ss) from data acquisition to product generation.

MODIS is an optical sensor, which has inherent limitations in observing sea ice and snow. Unlike a passive-microwave sensor, which can detect microwave energy through clouds, MODIS cannot observe the surface when cloud cover is present. MODIS products, therefore, have cloud masks built into the data arrays to prevent clouds from being interpreted as ice and snow.

MODIS provides global coverage every one to two days in 36 spectral bands. Spatial resolution of the MODIS data varies by band from 250 m to 1 km. By contrast, the Advanced Very High Resolution Radiometer (AVHRR) sensor has five spectral bands with a spatial resolution of 4 km or 1 km. For more information about MODIS, visit NASA's MODIS webpages.

The two grids are based on different map projections. The polar stereographic projection was initially used with ice concentration products developed at the NASA Goddard Space Flight Center (GSFC) and has been retained for historical consistency. It specifies a projection plane tangent to the earth at 70° latitude, which was selected so that little or no distortion would occur in the marginal ice zone.

The following table describes the data subsetting, reformatting, and reprojection services that are currently available for MODIS data via the NASA Earthdata Search tool.

This short article describes the customization services available for SMAP data using Earthdata Search.

This short article describes the customization services available for VIIRS data using Earthdata Search.

Assuming the data that were produced conform to the ML (25km) EASE-Grid definition, defined by the Ml.gpd and described in our Guide to EASE Grids, then you should be able to utilize the IDL tools that are distributed with our other EASE Grid geolocation tools.

There are five different levels of AMSR-E data, Level-0 through Level-4. Level-0 Reconstructed, unprocessed instrument/payload data at full resolution; any and all communications artifacts, for example, synchronization frames, communications headers, and duplicate data removed.

A variety of features can be detected in the RAMP image mosaic. SAR data allow ready discrimination between areas of high snow accumulation, crevassed regions, and areas susceptible to seasonal melt. Field camps and features such as runways and heavily traveled snowmobile tracks are also visible. The collection of images below demonstrates the degree of detail provided by the RAMP image mosaic. Please note the white and/or blue colors used in the annotations on the images are simply for better contrast against the background and have no other significance.

NSIDC has scripts that run several times a day. If new SNODAS files are found, these scripts will automatically post them to our FTP server. If you need data sooner than the normal timeframe that NSIDC uploads files to our FTP site, you can contact NOHRSC, as they distribute the data for operational users.

AMSR-E Slow Rotation Data is a research product distributed by the Japan Aerospace Exploration Agency (JAXA) that have been obtained with a slow rotation of AMSR-E's antenna at 2 rotations per minute (rpm).

Hierarchical Data Format (HDF) is the standard data format for all NASA Earth Observing System (EOS) data products.It is also known as HDF-EOS.

There are 40 laser shots in one second which are associated with the transmit pulses from the ICESat/GLAS instrument. The first shot is from the laser, the last shot is the 40th record of that transmitted pulse. The GLAS Altimetry Product Usage Guidance  document explains it like this: "Thirty-nine delta times are provided, which the user adds to the full UTC time of the first transmit time in each record, to calculate the 40 laser shot times." Last Updated April 2020

The Normalized Difference Snow Index (NDSI) snow cover is an index that is related to the presence of snow in a pixel and is a more accurate description of snow detection as compared to Fractional Snow Cover (FSC). Snow typically has very high visible (VIS) reflectance and very low reflectance in the shortwave infrared (SWIR), a characteristic used to detect snow by distinguishing between snow and most cloud types. Snow cover is detected using the NDSI ratio of the difference in VIS and SWIR reflectance; NDSI = ((band 4-band 6) / (band 4 + band 6)).

The Network Common Data Form (NetCDF) file format was developed by the Unidata project at the University Corporation for Atmospheric Research (UCAR). NetCDF (network Common Data Form) is a set of interfaces for array-oriented data access and a freely distributed collection of data access libraries for C, Fortran, C++, Java, and other languages. The netCDF libraries support a machine-independent format for representing scientific data.

Surface roughness greatly affects the elevation measurement accuracy. Over most of the ice sheets, the accuracy of each elevation measurement is 15 cm. Average ice elevation changes less than 1 cm will be detected by averaging the elevation differences observed at many points in selected regions of the ice sheets. Over land, the vertical accuracy of the elevation measurements will be better than a meter in regions of low slope and up to 10 m in regions of large slopes.

The standard waveform fit is optimized for "ice sheet-like" returns. The majority of these are single-peaked, narrow waveforms. The standard fit allows for only two peaks. Alternate waveform fitting is meant to capture up to six peaks. More peaks are necessary for more complex waveforms over land, vegetated surfaces and crevassed parts of ice sheets and glaciers. Another key difference between standard and alternate fit concerns the noise floor threshold.