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Description
The SMAP mission objective is to provide global measurements of soil moisture and its freeze-thaw state. SMAP measures the amount of water in the top 5 cm (2 inches) of soil everywhere on the Earth’s surface every three days. These data are useful for:
- Further understanding of processes that link the water, energy, and carbon cycles
- Enhance weather and climate prediction models
- Quantify net carbon flux in boreal landscapes
- Develop improved flood-prediction and drought-monitoring capabilities
The SMAP spacecraft instrumentation features an L-band radiometer and L-band synthetic aperture radar (SAR), measuring surface emissions and backscatter and sensing soil conditions through moderate vegetation cover.
Level-1 SAR data products from the SMAP mission are available through the Alaska Satellite Facility DAAC. Level-1 through Level-4 radiometer data and Level-2 and Level-3 radar data are available from the National Snow and Ice Data Center DAAC. In 2015, a failure of the radar power supply caused the SAR sensor to stop operating. Therefore, active SAR data are only available for April 13 – July 7, 2015. More information on the anomaly is available from JPL.
SMAP Synthetic Aperture Radar Overview
| Dataset Property | Value |
|---|---|
| Temporal Coverage | April 13 – July 7, 2015 |
| Repeat Cycle | 3 days at the equator and 2 days at boreal latitudes (>45 degrees N). |
| Spatial Coverage | Worldwide |
| Center Frequency | L-Band (1.2 to 1.3 GHz) |
| Spatial Resolution | • 1-3 km over the outer 70% of the swath (L1C_S0_HiRes product) • Approximately 5 km x 30 km (L1B_S0_LoRes product) |
| Swath Width | 1,000 km |
| Polarizations | VV, HH, HV |
| File format | HDF5 |
| Provider | NASA Jet Propulsion Laboratory (JPL) |
| License | See License and Data Citation tab |
| Download info | Data Discovery |
| Date published: | April 2015 |
Product Summary
Citation
Citation is critically important for dataset documentation and discovery. This dataset is openly shared, without restriction, in accordance with the EOSDIS Data Use Policy.
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Data Center Citation
Citing SMAP Level 1 Datasets
Cite datasets in publications such as journal papers, articles, presentations, posters, and websites. Each SMAP Level 1 dataset has an assigned DOI. Please also send a copy of publications that cite datasets or tools obtained through ASF to uso@asf.alaska.edu.
Crediting SMAP Imagery
Include appropriate credit with each image shown in publications such as journal papers, articles, presentations, posters, and websites. For more information, see NASA guidelines.
| Format | Example |
|---|---|
| SMAP data [year of data acquisition] (NASA). Dataset: [name of dataset]. Retrieved from ASF [add URL if print publication: asf.alaska.edu] DAAC [day month year of data access]. DOI: [doi] | SMAP data 2015 (NASA). Dataset: SMAP SMAP_L1B_S0_LoRes_V2. Retrieved from ASF DAAC 7 December 2015. DOI: https://doi.org/10.5067/j4szzv52b88j |
SMAP Level 1 Datasets and DOIs
| Dataset | DOI |
|---|---|
| L1A Radar | 10.5067/DM0U37IYZ6NK |
| L1B_S0_LoRes | 10.5067/NEWTOCOKVZHF |
| L1C_S0_HiRes | 10.5067/NVVUJ0MNG3PN |
| SMAP_L1A_Radar_V2 | 10.5067/O383X9CEPGWV |
| SMAP_L1B_S0_LoRes_V2 | 10.5067/J4SZZV52B88J |
| SMAP_L1C_S0_HiRes_V2 | 10.5067/CBUK530QAO9M |
| SMAP_L1A_Radar_RO | 10.5067/STFA3C0ZSXNC |
| SMAP_L1B_S0_LoRes_V3 | 10.5067/UCZC0LUSSQ0I |
| SMAP_L1C_S0_HiRes_V3 | 10.5067/E0QIAMXM89YY |
File Naming Convention
SMAP – Data, Imagery, and Naming Conventions
Data Acquisition and Processing
Low Rate, Low Resolution
Low-resolution radar data and low-rate radiometer data will be acquired continuously over fore and aft portions of the scan (full 360 degrees) and ascending and descending portions of the orbit.
High Resolution
High-resolution radar data will be acquired to include, at a minimum:
- 360 degrees of the antenna scan (fore and aft looks) for the morning (6 a.m. equator crossing) half orbit over the global land region (excluding the Antarctic)
- 180 degrees of the antenna scan (fore look) for the evening (6 p.m. equator crossing) half orbit over the boreal land region (north of 45-degrees N latitude)
- 180 degrees of the antenna scan (fore look) for the morning half orbit over the coastal ocean region (within 1,000 km of continental boundaries)
The Science Operations Phase (SOP) begins after completion of the 90-day post-launch in-orbit commissioning and lasts for 3 years. The first part of the SOP is the 12-month Calibration and Validation (Cal/Val) phase. Next is the 24-month Routine Observations Phase (ROP).
Processing
The SMAP science-data products will be generated on the SMAP Science Data System using science software developed on the SDS Testbed. Processing will take place at the Jet Propulsion Laboratory (JPL) in Pasadena, California. Products will be distributed to two NASA Distributed Active Archive Centers (DAACs), ASF and the National Snow and Ice Data Center (NSIDC), for distribution to the science community.
The science software is based on algorithms for each product described in the Algorithm Theoretical Basis Documents (ATBDs).
SMAP products are processed at Levels 1, 2, 3, and 4. ASF distributes Level 1 radar products. See the Instrument events timetable
The SMAP baseline science-data products are publicly available through two NASA-designated data centers, the Alaska Satellite Facility (ASF) and the National Snow and Ice Data Center (NSIDC) DAAC. ASF will distribute the Level 1 radar products and NSIDC will distribute the radiometer and Level 2-4 products. All products will conform to the HDF-5 standard.
SMAP synthetic aperture radar (SAR) data have a spatial resolution of 1-3 km over the outer 70% of the swath (L1C_S0_HiRes product). The low-resolution radar data are ‘slices’ of resolution approximately 5 km x 30 km (L1B_S0_LoRes product). The radiometer data have a spatial resolution (IFOV) of 39 km x 47 km, nominally referred to as 40-km resolution (L1B_TB product). The L1C_TB data products are resampled TB data on a 36-km Earth grid and will have spatial resolution ~10% greater than the L1B_TB data (depending on the resampling method).
SMAP science-data products will be generated on the Science-Data System production system using science software developed on the SDS Testbed. The science software is based on algorithms for each product described in the Algorithm Theoretical Basis Documents (ATBDs).
| Short Name | Description | Gridding (km) | Latency* | ATBD** | Product Spec Doc | Source |
|---|---|---|---|---|---|---|
| L1A_Radar | Raw radar data in time order (half orbit) | – | 12 hrs | n/a | View | ASF |
| L1A_Radiometer | Radiometer raw data in time order | – | 12 hrs | n/a | NSIDC | |
| L1B_S0_LoRes | Low-resolution radar σ ο in time order (half orbit) | 5×30 | 12 hrs | View | View | ASF |
| Backscatter analysis document | ||||||
| L1B_TB | Radiometer TB in time order | 36×47 | 12 hrs | View | NSIDC | |
| L1C_S0_HiRes | High-resolution radar σ ο (half orbit gridded) | 1 | 12 hrs | View | View | ASF |
| Backscatter analysis document | (1-3)*** | |||||
| L1C_TB | Radiometer T B (half orbit, gridded) | 36 | 12 hrs | View | NSIDC | |
| L2_SM_A | Soil moisture (radar, half orbit) | 3 | 24 hrs | View | NSIDC | |
| L2_SM_P | Soil moisture (radiometer, half orbit) | 36 | 24 hrs | View | NSIDC | |
| L2_SM_A/P | Soil moisture (radar/radiometer, half orbit) | 9 | 24 hrs | View | NSIDC | |
| L3_F/T_A | Freeze-thaw state (radar, daily composite) | 3 | 50 hrs | View | NSIDC | |
| L3_SM_A | Soil moisture (radar, daily composite) | 3 | 50 hrs | View | NSIDC | |
| L3_SM_P | Soil moisture (radiometer, daily composite) | 36 | 50 hrs | View | NSIDC | |
| L3_SM_A/P | Soil moisture (radar/radiometer, daily composite) | 9 | 50 hrs | View | NSIDC | |
| L4_SM | Soil moisture (surface and root zone) | 9 | 7 days | View | NSIDC | |
| L4_C | Carbon net ecosystem exchange (NEE) | 9 | 14 days | View | NSIDC |
*Mean latency under normal operating conditions (defined as time from data acquisition by the observatory to availability to the public data archive).
**Algorithm Theoretical Basis Documents (ATBDs) provide the physical and mathematical descriptions of the algorithms used in the generation of science-data products. The ATBDs include a description of variance and uncertainty estimates and considerations of calibration and validation, exception control, and diagnostics. Internal and external data flows are also described.
***Over outer 70% of swath
Ancillary Data Reports
The SMAP Ancillary Data Reports below hold application-related descriptions of datasets used with science-algorithm software in generating SMAP science-data products, as well as links to EASE grid information relevant to SMAP products.
These reports may undergo additional updates as new ancillary datasets or processing methods become available.
| Data Reports | Ancillary Data Examples | Main Ancillary Data Cited |
|---|---|---|
| Crop Type | Image | USDA Cropland Data ECOCLIMAP (global database of land surface parameters) |
| Landcover | Image | MODIS Land Cover Type (NASA Moderate Resolution Imaging Spectroradiometer) |
| Digital Elevation Model | Image | JPL Global Digital Elevation Model |
| Soil Attributes | Image | Harmonized World Soil Database |
| Static Water Fraction | Image | MODIS Water Mask |
| Urban Area | Image | Gridded Population of the World (GRUMP) |
| Vegetation Water Content | Image | Normalized Difference Vegetation Index (NDVI) |
| Permanent Ice | Image | MODIS Products Table |
| Precipitation | Image | ECMWF (European Centre for Medium-Range Weather Forecasts) |
Naming Convention — Level 1 Products:
All SMAP Level 1 products represent half orbits. Half-orbit boundaries take place at the northernmost and the southernmost spacecraft location in each orbital path. The most critical identifiers for these products are the orbit number and the designator that specifies the half of the orbit represented by the data.
The following template should be employed to name all SMAP Level 1 products. Note that the orbit number and the half-orbit designator provide the major means of identification.
SMAP_[Product ID]_[Orbit Number]_[A/D]_[First Date/Time Stamp]_[File Version ID].[extension]
Product ID:
The Product ID is based on the Short Name for each SMAP data product—for example: L1A_RADAR. See the table above.
Orbit Number:
A 5-digit orbit number beginning with orbit 00000 on launch. Leading zeros will be used to complete the 5-digit number.
The Half-Orbit Designator:
Division of SMAP orbits into half orbits takes place at the northernmost and southernmost point on the spacecraft path.
“A” indicates ascending; “D” is for descending.
First Date/Time Stamp:
The UTC date/time stamp of the first data element that appears in the product. Format is: YYYYMMDDThhmmss
File Version ID:
A 3-digit number that indicates the version of the data product for the specified half orbit.
Extension:
The products are in HDF5 format; the extension will be .h5.
Example File Names:
SMAP_L1B_TB_00934_A_20141225T074951_003.h5 (ascending)
SMAP_L2_SM_P_01512_D_20150206T210504_005.h5 (descending)