SMAP – ASF SMAP User Guide

Dataset Overview

  • SMAP products will be processed to Levels 1, 2, 3, and 4. 
  • ASF will distribute Level 1 radar products. 

Program Management

  • SMAP is a mission within the NASA Earth Systematic Mission (ESM) Program managed by Goddard Space Flight Center (GSFC). The Jet Propulsion Laboratory (JPL) is responsible for the overall success of the SMAP project.

Mission Objectives

  • SMAP is an Earth satellite mission designed to measure and map Earth’s soil moisture and freeze-thaw state to better understand terrestrial water, carbon, and energy cycles.
  • The goal is to combine the attributes of the radar and radiometer observations (in terms of their spatial resolution and sensitivity to soil moisture, surface roughness, and vegetation) to estimate soil moisture at a resolution of 10 km, and freeze-thaw state at a resolution of 1-3 km.
  • Using an advanced radar and radiometer, the satellite will be able to peer beneath clouds, vegetation, and other surface features to monitor water and energy fluxes. Data from the 3-year mission will help improve flood predictions and drought monitoring, and it will play a crucial role in understanding changes in water availability, food production, and other socioeconomic impacts of climate change.


Observatory

  • The SMAP observatory employs a dedicated spacecraft with an instrument suite launched on an expendable launch vehicle into a 680-km, 98-degree, near-polar, sun-synchronous orbit, with equator crossings at 6 a.m. and 6 p.m. local time.

Instrument

  • The SMAP instrument includes a radiometer and a synthetic aperture radar (SAR) operating at L-band (1.20-1.41 GHz). The instrument is designed to make coincident measurements of surface emission and backscatter, with the ability to sense the soil conditions through moderate vegetation cover. The instrument measurements will be analyzed to yield estimates of soil moisture and freeze-thaw state. The measurement swath width is 1,000 km, providing global coverage within 3 days at the equator and 2 days at boreal latitudes (>45 degrees N).

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).

Data Description


ASF will ingest, distribute, archive, and support post-launch Level 1 radar products for the SMAP mission. ASF will receive the Level 1 radar products from the SMAP Science Data System at the Jet Propulsion Laboratory (JPL) in Pasadena, California (Table 1).

SMAP Science Data Products at ASF DAAC

SMAP Mission Short Name DAAC Short Name Description File Size (MB) Files/Day
L1A_Radar SPL1AA Parsed Radar Telemetry 2,965 30
L1B_S0_LoRes SPL1BS0 Low Resolution radar σο in Time Order 300 30
L1C_S0_HiRes SPL1CS0 High Resolution Radar σο on Swath Grid 1,557 30

SMAP synthetic aperture radar 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).

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)

Using SMAP Products

Content will be available upon release of SMAP products.

Data Access

Following a post-launch checkout period, all data will be made available to the user community. Data are available under NASA’s data policy. There will be no period of exclusive access to NASA Earth science data.

The SMAP mission will make science-data products available to the public through two NASA-designated Earth science data centers, the ASF DAAC (for Level 1 radar products) and the NSIDC DAAC (for all other products).

To obtain SMAP data from ASF, view and download SMAP Level 1 radar data at ASF’s website:

Details on accessing data, including other DAAC synthetic aperture radar (SAR) datasets, are in ASF’s Get Started guide.

Acronyms and Abbreviations

The following acronyms and abbreviations are used in this document

Sample ID Heading 1
ASF Alaska Satellite Facility
ATBDs Algorithm Theoretical Basis Documents
Cal/Val Calibration and Validation
DAAC Distributed Active Archive Center
HDF5 Hierarchical Data Format
JPL Jet Propulsion Laboratory
NASA National Aeronautics and Space Administration
NSIDC National Snow and Ice Data Center
ROP Routine Observations Phase
SMAP Soil Moisture Active Passive
SAR Synthetic Aperture Radar
SDS Science Data System
SOP Science Operations Phase
UTC Coordinated Universal Time

Last updated: December 16, 2013

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