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Data Set ID:
AQ3_MCSM

Aquarius L3 Gridded 1-Degree Monthly Soil Moisture Climatology, Version 4

This data set contains Level-3 gridded monthly global soil moisture climatology estimates derived from the NASA Aquarius passive microwave radiometer on the Satélite de Aplicaciones Científicas (SAC-D).

Version Summary:

Initial Version

Geographic Coverage

Parameter(s):
  • Soils > Soil Moisture/Water Content
Spatial Coverage:
  • N: 90, S: -90, E: 180, W: -180

Spatial Resolution:
  • 1 Degree x 1 Degree
Temporal Coverage:
  • 25 August 2011 to 31 May 2015
Temporal Resolution: 1 month
Data Format(s):
  • HDF
  • XML
Platform(s) SAC-D
Sensor(s): AQUARIUS_RADIOMETER
Version: V4
Data Contributor(s): Rajat Bindlish, Thomas Jackson
Data Citation

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.

Bindlish, R. and T. Jackson. 2015. Aquarius L3 Gridded 1-Degree Monthly Soil Moisture Climatology, Version 4. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/Aquarius/AQ3_MCSM.004. [Date Accessed].

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Detailed Data Description

Format

The data files are in Hierarchical Data Format 5 (HDF5). The values are stored as bytes, 2-byte integers, or 4-byte floats. Data are 32-bit float. The palette object is 8-bit unsigned integer. Each data file is paired with an associated XML file. XML files contain file level metadata and location, platform, and campaign information.

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File and Directory Structure

Data are available on the HTTPS site in the https://n5eil01u.ecs.nsidc.org/AQUARIUS/ directory. Data files are organized into directories by time period: Monthly and Seasonal:

/AQ3_MCSM.004/
/AQ3_SCSM.004/

Within each directory, folders are organized by date, for example:

/2011.08.25/
/2012.03.21/

Folders contain HDF5 and XML (.xml) files.

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File Naming Convention

File names correspond to those of their parent Aquarius binned data products, indicating the binning periods as part of the names.

Files are named according to the following conventions and as described in Table 1:

Q20112442014273.L3m_MC_SOILM_V4.0_rad_sm_1deg

QYYYYDDDyyyyddd.L3m_tttt_SOILM_vvvv_rad_sm_1deg

Where:

Table 1. File Naming Convention
Variable Description
Q Indicates Aquarius instrument
YYYY Year climatology start
DDD Day climatology start
yyyy Year climatology end
ddd Day climatology end
L3m Processing level
tttt

Binning period length, where:

MC = Monthly Climatology
SCAU = Seasonal Climatology Autumn
SCSP = Seasonal Climatology Spring
SCSU = Seasonal Climatology Summer

SOILM Geophysical parameter: SOILM = soil moisture
vvvv Data version, example: V4.0
rad_sm_1deg 1-degree radiometer soil moisture

Each data file is paired with an XML file of the same name with .xml extension. The XML file contains metadata associated with the data file.

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File Size

Data files are approximately 263 KB each.

XML files are approximately 3 KB each.

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Volume

Data Volume for Aquarius L3 Monthly Soil Moisture Climatologies is approximately 4 MB.

Data Volume for Aquarius L3 Seasonal Soil Moisture Climatologies is approximately 2 MB.

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Spatial Coverage

Spatial coverage is global.

Spatial Resolution

Spatial resolution of the L3 data is 1 degree.

Projection and Grid Description

The l3m_data object is a two-dimensional array (180 rows, 360 columns) of an Equidistant Cylindrical (also known as Plate Carrée) projection of the globe.

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Temporal Coverage

AQ3_MCSM: 25 August 2011 to 31 May 2015

AQ3_SCSM: 25 August 2011 to 07 June 2015

Monthly climatology products contain the mean soil moisture values of composites for the mission.

  • August 25, 2011 to August 31, 2014
  • September 1, 2011 to September 30, 2014
  • October 1, 2011 to October 31, 2014
  • November 1, 2011 to November 30, 2014
  • December 1, 2011 to December 31, 2014
  • January 1, 2012 to January 31, 2015
  • February 1, 2012 to February 28, 2015
  • March 1, 2012 to March 31, 2015
  • April 1, 2012 to April 30, 2015
  • May 1, 2012 to May 31, 2015
  • June 1, 2012 to June 30, 2014
  • July 1, 2012 to July 31, 2014

Seasonal climatology products are defined between equinox and solstice. The file names contain the exact DOY for each season. For example: the file Q20113552015079.L3m_SCWI_SOILM_V4.0_rad_sm_1deg contains the data for Winter composites ranging from 2011 DOY 355 (21 December) to 2015 DOY 079 (20 March).

Seasonal climatology products contain the mean soil moisture values for the following composites for the mission:

  • June 21, 2011 to September 20, 2014, includes mean value for Summer 2011, Summer 2012, Summer 2013, and Summer 2014.
  • September 21, 2011 to December 20, 2014, includes mean value for Autumn 2011, Autumn 2012, Autumn 2013, Autumn 2014.
  • December 21, 2011 to March 20 2015, includes mean value for Winter 2011, Winter 2012, Winter 2013, Winter 2014, and Winter 2015.
  • March 21, 2012 to June 07, 2015, includes mean value for Spring 2012, Spring 2013, Spring 2014, and Spring 2015.

NOTE: Due to a power failure on the Satélite de Aplicaciones Científicas (SAC)-D spacecraft on 08 June 2015, data from NASA's Aquarius instrument were no longer being produced after 07 June 2015. Accordingly, the date range for the climatology Spring season ends on 07 June 2015, rather than extending through the full Spring season.

Temporal Resolution

Monthly, Seasonal

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Parameter or Variable

The L3 products are representations of binned data products generated from Aquarius data. The data object, l3m_data, represents a mean Soil Moisture value of all composites for the mission at each grid point. The grid resolution is 1 degree.

Parameter Description

Each L3 soil moisture product contains the l3m_data object, with attributes described in Table 2.

Table 2. L3 Soil Moisture l3m_data Object Attributes
Name Value
Scaling linear
Scaling Equation (Slope*l3m_data) + Intercept = Parameter value
Slope 1.0
Intercept 0
_FillValue -32767.0
add_offset 0.0
scale_factor 1.0

The palette object included in the data file is the color palette used in graphics generated from the mapped files. The user can either use this palette or any palette of their choice.

Metadata are included as global attributes. Table 3 lists the global attribute names and the values from data file Q20112442014273.L3m_MC_SOILM_V4.0_rad_sm_1deg. Values that vary from granule to granule are noted.

Table 3. L3 Soil Moisture Metadata General Attributes
Name Value
Product Name Q20112442014273.L3m_MC_SOILM_V4.0_rad_sm_1deg
Sensor Name Aquarius
Sensor Aquarius
Title Aquarius Level-3 Standard Mapped Image
Data Center NASA/GSFC OBPG
Mission SAC-D Aquarius
Mission Characteristics Nominal orbit: inclination=98.0 (Sun-synchronous); node=6PM (ascending); eccentricity=<0.002; altitude=657 km; ground speed=6.825 km/sec
Sensor Characteristics Number of beams=3; channels per receiver=4; frequency 1.413 GHz; bits per sample=16; instantaneous field of view=6.5 degrees; science data block period=1.44 sec
Product Type MC
Processing Version V4.0
Software Name smigen
Software Version 5.04
Processing Time 2015166164053000 (varies)
Input Files Q20112442014273.L3b_MC_SOILM_V4.0.main (varies)
Processing Control smigen par=Q20112442014273.L3m_MC_SOILM_V4.0_rad_sm_1deg.param (varies)
Input Parameters ifile = Q20112442014273.L3b_MC_SOILM_V4.0.main|ofile = Q20112442014273.L3m_MC_SOILM_V4.0_rad_sm_1deg|prod = rad_sm|palfile = /sdps/sdpsoper/Science/OCSSW/V2015.2/data/common/palette/sm.pal|processing version = V4.0|meas = 1|stype = 1|datamin = 0.000000|datamax = 0.400000|lonwest = -180.000000|loneast = 180.000000|latsouth = -90.000000|latnorth = 90.000000|resolution = 1deg|projection = RECT|gap_fill = 0|seam_lon = -180.000000|minobs = 0|deflate = 4|oformat = HDF5|precision = F|
L2 Flag Names POINTING,NAV,LANDRED,ICERED,REFL_1STOKESMOONRED,REFL_1STOKESGAL,TFTADIFFRED, RFI_REGION,SAOVERFLOW,COLDWATERRED,WINDRED,TBCONS
Period Start Year 2011
Period Start Day 244 (varies)
Period End Year 2014 (varies)
Period End Day 274 (varies)
Start Time 2011244021854088 (varies)
End Time 2014274004423594 (varies)
Start Year 2011 (varies)
Start Day 244 (varies)
Start Millisec 8334088 (varies)
End Year 2014 (varies)
End Day 275 (varies)
End Millisec 2663594 (varies)
Start Orbit 1214
End Orbit 17781
Map Projection Equidistant Cylindrical
Latitude Units degrees North
Longitude Units degrees East
Northernmost Latitude 90.0
Southernmost Latitude -90.0
Westernmost Longitude -180.0
Easternmost Longitude 180.0
Latitude Step 1.0
Longitude Step 1.0
SW Point Latitude -89.5
SW Point Longitude -179.5
Data Bins 11021
Number of Lines 180
Number of Columns 360
Parameter Soil Moisture
Measure Mean
Units m3/m3
Scaling linear
Scaling Equation (Slope*l3m_data) + Intercept = Parameter value
Slope 1.0
Intercept 0.0
Data Minimum 0.02
Data Maximum 0.85605
Suggested Image Scaling Minimum 0.0
Suggested Image Scaling Maximum 0.4
Suggested Image Scaling Type LINEAR
Suggested Image Scaling Applied No
_lastModified 2015166164053000

Sample Data Record

Below is a sample of the l3m_data soil moisture climatology data array from the file: Q20112442014273.L3m_MC_SOILM_V4.0_rad_sm_1deg.

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Software and Tools

HDF-aware software must be used to read the Aquarius soil moisture files. The following external links provide access to software for reading and viewing HDF5 data files. Please be sure to review instructions on installing and running the programs.

HDFView: Visual tool for browsing and editing HDF4 and HDF5 files.

Panoply netCDF, HDF and GRIB Data Viewer: Cross-platform application. Plots geo-gridded arrays from netCDF, HDF and GRIB data sets.

For additional tools, see the HDF5 Tools and Software Web site.

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Data Acquisition and Processing

Theory of Measurements

The Aquarius SCA algorithm uses the L-band horizontally polarized (h-pol) brightness temperature observations due to the higher sensitivity of this channel to soil moisture. The Aquarius SCA approach is based on the simplified radiative transfer model developed under the assumption that the canopy and soil temperatures are the same (Jackson 1993). The SCA is applied to the individual Aquarius footprint Level-2 brightness temperature observations to produce a swath-based time-order product. (Bindlish and Jackson, 2013Bindlish et al, 2013). Details on these steps are provided in the Aquarius L2 Soil Moisture documentation.

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Data Acquisition Methods

Aquarius L3 Gridded 1-Degree Soil Moisture Climatology data are generated from measurements derived from the Aquarius Level-2 Soil Moisture product. Each climatology product contains data from one time period, monthly or seasonally. The best quality data are selected for each orbit during Level-0 to Level-1A data processing and are then used to create the Level-2 file that is input to the L3 science file.

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Derivation Techniques and Algorithms

The Aquarius L3 gridding algorithm uses local polynomial fitting to grid the Level-2 soil moisture retrievals on a 1 degree grid (Fan and Gijbels, 1996Lilly and Lagerloef, 2008). The L3 processing of Aquarius satellite data takes measurements at the boresight locations of the three radiometer beams, which have been already converted into physical units of soil moisture, and maps these onto a 1 degree grid.

This method fits a Pth-order polynomial at each grid point xm. For data values gn observed at locations xn, n=1, 2,…N, this corresponds to minimizing

Equation 1

at every grid point x=xm, where

decaying weighting function

is a decaying weighting function which depends upon the bandwidth h, with K(x) being a probability distribution function.

The regression coefficients

regression coefficients

p=1, 2,…P vary with spatial location, and are estimated at all grid point locations.

The function g(x) is estimated by the lowest order coefficient,

lowest order co-efficient

while higher-order regression coefficients estimate the derivatives of the field through

higher order regression co-efficients

The above discussion focuses on a 1-dimensional application, but can be extended to a 2-dimensional application. A complete description for the 2-dimensional problem is available in Fan and Gijbels, 1996Lilly and Lagerloef, 2008.

Processing Steps

Aquarius L3 Gridded 1-Degree Soil Moisture Climatology data are produced by NASA Goddard Space Flight Center's Ocean Data Processing System (ODPS).

Each product represents data binned over the period covered by the original Aquarius product. The mean for the observation period is used to obtain the values for the grid points from the binned data products. Each product contains one soil moisture image and is stored in one physical HDF file. The data are not filtered during the gridding process. The user is advised to refer to the flags in the Aquarius Level-2 Soil Moisture product.

Monthly Climatology products are the mean value of all monthly composites for the mission, for example:
(January 2012 + January 2013 + January 2014) / 3

Seasonal Climatology products are the mean value of all seasonal composites for the mission, for example:
(Spring 2012 + Spring 2013 + Spring 2014) / 3

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Sensor or Instrument Description

Aquarius/SAC-D is a collaboration between NASA and Argentina's space agency, Comisión Nacional de Actividades Espaciales (CONAE), with participation from Brazil, Canada, France and Italy. The Aquarius instrument was built jointly by NASA's Jet Propulsion Laboratory and NASA's Goddard Space Flight Center.

The Aquarius instrument includes three radiometers and one scatterometer. The soil moisture data are collected by the radiometers. The radiometers measure brightness temperature at 1.414 GHz in the horizontal and vertical polarizations (TH and TV). The scatterometer is a microwave radar sensor that measures backscatter for surface roughness corrections. Table 4 summarizes instrument characteristics.

Table 4. Aquarius Instrument Characteristics
Instrument Characteristics
3 radiometers in push-broom alignment
  • Frequency: 1.413 GHz
  • Band width: less than or equal to 26 MHz
  • Swath Width: 390 km
  • Science data block period: 1.44 sec
  • Footprints for the beams are: 74 km along track x 94 km cross track, 84 x 120 km, and 96 x 156 km, yielding a total cross track of 390 km.
  • Beam incidence angles of 29.36, 38.49, and 46.29 degrees incident to the surface. Beams point away from the sun.
Scatterometer
  • Frequency: 1.26 GHz
  • Band Width: 4 MHz
  • Swath Width: 390 km
  • Science data block period: 1.44 sec

SAC-D spacecraft Orbit Parameters:

  • 98 minute sun-synchronous
  • 6 PM ascending orbit, 6 AM descending orbit
  • 657 km equatorial altitude (655 km minimum, 685 km maximum over the orbit)
  • Ground-track repeat interval: Weekly, 103 orbits
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References and Related Publications

Contacts and Acknowledgments

Rajat Bindlish
NASA Goddard Space Flight Center
Hydrological Sciences Laboratory
Code 617, Bldg 33, G216
Greenbelt, MD 20771 USA

Thomas Jackson
United States Department of Agriculture
Agricultural Research Service
Hydrology and Remote Sensing Laboratory
Beltsville, MD 20705 USA

Acknowledgments: 

This work was funded by NASA under the Interagency agreement NNH10AN10I. Tianjie Zhao helped with development of the soil moisture algorithm. The support provided by Michael Cosh, Peggy O'Neill, Thomas Holmes and Wade Crow is acknowledged. We acknowledge the support provided by Gary Lagerloef, David Le Vine, Gene Feldman and the Aquarius Data Processing System group in the implementation of the Aquarius Soil moisture algorithm.

Document Information

DOCUMENT CREATION DATE

01 October 2015

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