Data Set ID:
NSIDC-0738

SMAP Radiometer Twice-Daily rSIR-Enhanced EASE-Grid 2.0 Brightness Temperatures, Version 1

This data set contains twice-daily, enhanced-resolution brightness temperature data derived from the SMAP radiometer. Data are available on the Northern Hemisphere, Southern Hemisphere, Temperate, and Mid-Latitude (sub-set of Global) EASE-Grid 2.0 projections and on the 25 km, 3.125 km, 36 km, 09 km, and 03 km resolution grids. This data set applies the same SIR technique used to derive brightness temperatures from the SMMR, AMSR-E, and SSM/I-SSMIS sensors and is a companion product for the MEaSUREs Calibrated Enhanced-Resolution Passive Microwave Daily EASE-Grid 2.0 Brightness Temperature ESDR data set (DOI: 10.5067/MEASURES/CRYOSPHERE/NSIDC-0630.001).

This is the most recent version of these data.

Version Summary:

Initial release

STANDARD Level of Service

Data: Data integrity and usability verified

Documentation: Key metadata and user guide available

User Support: Assistance with data access and usage; guidance on use of data in tools

See All Level of Service Details

Parameter(s):
  • MICROWAVE > BRIGHTNESS TEMPERATURE
Data Format(s):
  • NetCDF
Spatial Coverage:
N: 90, 
S: -90, 
E: 180, 
W: -180
Platform(s):SMAP
Spatial Resolution:
  • Varies x Varies
Sensor(s):SMAP L-BAND RADIOMETER
Temporal Coverage:
  • 31 March 2015 to 6 April 2019
Version(s):V1
Temporal Resolution12 hourMetadata XML:View Metadata Record
Data Contributor(s):Mary Brodzik, David Long, Molly Hardman

Geographic Coverage

Other Access Options

Other Access Options

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As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Brodzik, M. J., D. G. Long, and M. A. Hardman. 2019. SMAP Radiometer Twice-Daily rSIR-Enhanced EASE-Grid 2.0 Brightness Temperatures, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/QZ3WJNOUZLFK. [Date Accessed].
Created: 
28 August 2019
Last modified: 
19 September 2019

Data Description

Parameters

The main parameter for this data set is Brightness Temperature (Tb), measured in kelvins (K).

File Information

Format

Data are provided in netCDF (.nc) format. 

Extensible Markup Language (.xml) files with associated metadata are also provided.

File Contents

Parameter Description Units Scale Factor Fill Value Missing Value
Table 1. Parameters
TB Brightness Temperature (Tb) kelvin (K) 0.01 0.0 60000
TB_time Average time of the measurements used to derive Tb Minutes since 00:00:00 on the day of measurement 1.00 -32768 Not used
TB_std_dev Standard deviation of the measurements used to derive Tb kelvin (K) 0.01 65535 65534 (only used when Tb is set to missing value)
TB_num_samples Number of measurements used to derive Tb count N/A 0 Not used
Incidence_angle Average incidence angle of the measurements used to derive Tb degrees (°) 0.01 -0.0 Not used

Naming Convention

Data files are named according to the following convention and as described in Table 1:
NSIDC-0738-EASE2_[G][###km]-[SMAP_LRM]-yyyyddd-[channel]-[pass]-[algorithm]-JPL-v##.nc

Table 2. File Naming Convention
Variable Description
NSIDC-0738 NSIDC unique data set identifier
EASE2 Indicates the data use the EASE-Grid 2.0 projection
G Grid:
N  = Northern
S = Southern
T = Temperate & Tropical
M = Mid-latitudes
###km Resolution of the data, values range from 3.125 km to 36 km
SMAP_LRM Indicates the data are derived from the SMAP L-band radiometer
yyyyddd Date in year-day-of-year format
channel Channel (frequency + polarization), possible polarizations include:
V = vertical
H = horizontal
F = fourth Stoke's parameter
pass The direction or local time-of-day of the satellite pass:
A = Asecending (T or M grids only)
D = Descending (T or M grids only)
M = Morning (N or S grids only)
E = Evening (N or S grids only)
algorithm Specifies the algorithm use for the image reconstruction:
GRD = drop-in-the-bucket
SIR = radiometer version of Scatterometer Image Reconstruction
JPL Indicates the data were produced at the NASA Jet Propulsion Laboratory
v## Data set version number

Example files: 
NSIDC-0738-EASE2_S25km-SMAP_LRM-2019095-1.4F-E-GRD-JPL-v1.0.nc
NSIDC-0738-EASE2_S25km-SMAP_LRM-2019095-1.4H-E-GRD-JPL-v1.0.nc

File Size

The average data file size is approximately 21.5 MB.

The entire data collection is approximately 2.7 TB.

Spatial Information

Coverage

The spatial coverage for the entire data set is global. However, spatial coverage varies between data files. Data are available on the Northern Hemisphere, Southern Hemisphere, Mid-Latitude, and Temperate & Tropical EASE-Grid 2.0 projections. 

Resolution

Spatial resolution varies by data file. Possible grid resolutions include: 3 km, 3.125 km, 9 km, 25 km, and 36 km.

Geolocation

Table 3 provides a description of the EASE-Grid 2.0 projections used in this data set. For a description of the various grids used in this data set, see the EASE Grids Map Projection and Grid web page. 

Table 3. Geolocation Details
Geographic coordinate system WGS 1984 WGS 1984 WGS 1984
Projected coordinate system EASE-Grid 2.0 Global (also applies to Temperate & Tropical and Mid-latitude projections) EASE-Grid 2.0 Northern Hemisphere EASE-Grid 2.0 Southern Hemisphere
Longitude of true origin 0 0 0
Latitude of true origin 30 90 -90
Scale factor at longitude of true origin N/A N/A N/A
Datum WGS 1984 WGS 1984 WGS 1984
Ellipsoid/spheroid WGS 1984 WGS 1984 WGS 1984
Units Meter Meter Meter
False easting 0 0 0
False northing 0 0 0
EPSG code 6933 6931 6932
PROJ4 string
+proj=cea +lon_0=0 +lat_ts=30 +x_0=0 +y_0=0 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs 
+proj=laea +lat_0=90 +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs 
+proj=laea +lat_0=-90 +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs 
Reference http://epsg.io/6933 http://epsg.io/6931 http://epsg.io/6932

Temporal Information

Coverage

31 March 2015 to 06 April 2019

Resolution

Twice-daily

Data Acquisition and Processing

Background

This data set applies the radiometer version of the Scatterometer Image Reconstruction (rSIR) technique to a new passive microwave sensor, the NASA SMAP radiometer. This technique was originally developed and applied to the SMMR, AMSR-E, and SSM/I-SSMIS sensors; it has now been used to produce enhanced-resolution and improved soil moisture data from the SMAP satellite. This data set is provided in the same format, with all the same high-quality metadata, as the MEaSUREs Calibrated Enhanced-Reoslution Passive Microwave Daily EASE-Grid 2.0 Brightness Temperature ESDR (NSIDC-0630) data set.

Acquisition

The input for this data set is the SMAP L1B Radiometer Half-Orbit Time-Ordered Brightness Temperatures, Version 4 (SPL1BTB) data set, minor version R16010. Using the quality flag on the input data set, all but the highest quality SPL1BTB measurements are removed.

Processing

This data set follows the same processing steps as the MEaSUREs (NSIDC-0630) data set. For more details, see the NSIDC-0630 user guide, Brodzik and Long (2016), or the paper by Long et al. (2019). 

Quality, Errors, and Limitations

For a more detailed description of this data set, see Long et al. 2019.

Instrumentation

Description

For a detailed description of the SMAP instrument, visit the SMAP Instrument page at the Jet Propulsion Laboratory (JPL) SMAP website.

Version History

This is the first version of this data set.

Related Data Sets

MEaSUREs Calibrated Enhanced-Resolution Passive Microwave Daily EASE-Grid 2.0 Brightness Temperature ESDR (NSIDC-0630)

SMAP L1B Radiometer Half-Orbit Time-Ordered Brightness Temperatures, Version 4 (SPL1BTB)

SMAP Data at NSIDC | Overview

Related Websites

SMAP at NASA JPL

Contacts and Acknowledgments

Mary J. Brodzik
National Snow and Ice Data Center
449 UCB
Boulder, CO 80309

David G. Long
Brigham Young University

Molly A. Hardman
National Snow and Ice Data Center
449 UCB
Boulder, CO 80309

References

Brodzik, M. J. and D. G. Long. 2016. Calibrated Passive Microwave Daily EASE-Grid 2.0 Brightness Temperature ESDR (CETB) Algorithm Theoretical Basis Document. MEaSUREs Project White Paper. NSIDC. Boulder, CO. Available at: https://nsidc.org/sites/nsidc.org/files/technical-references/MEaSUREs_CETB_ATBD_v1.0.pdf

Long, D. G., M. J. Brodzik, and M. A. Hardman. 2019. Enhanced-Resolution SMAP Brightness Temperature Image Products. IEEE Transactions on Geoscience and Remote Sensing 57(7), 4151-4163. https://dx.doi.org/10.1109/TGRS.2018.2889427

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