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Aquarius L3 Gridded 1-Degree Seasonal Soil Moisture Climatology, Version 4
This data set contains Level-3 gridded seasonal global soil moisture climatology estimates derived from the NASA Aquarius passive microwave radiometer on the Satélite de Aplicaciones Científicas (SAC-D).
Initial Version
Geographic Coverage
Spatial Coverage: |
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Spatial Resolution: |
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Temporal Coverage: |
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Temporal Resolution: | 3 month |
Parameter(s): |
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Platform(s) | SAC-D |
Sensor(s): | AQUARIUS_RADIOMETER |
Data Format(s): |
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Version: | V4 |
Data Contributor(s): | Rajat Bindlish, Thomas Jackson |
Metadata XML: | View Metadata Record |
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 Seasonal 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_SCSM.004. [Date Accessed].Detailed Data Description
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.
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.
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:
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 |
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.
Data files are approximately 263 KB each.
XML files are approximately 3 KB each.
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.
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.
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
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.
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.
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
.
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.
Data Acquisition and Processing
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, 2013; Bindlish et al, 2013). Details on these steps are provided in the Aquarius L2 Soil Moisture documentation.
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.
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, 1996; Lilly 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
at every grid point x=xm, where
is a decaying weighting function which depends upon the bandwidth h, with K(x) being a probability distribution function.
The 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,
while higher-order regression coefficients estimate the derivatives of the field through
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, 1996; Lilly 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
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.
Instrument | Characteristics |
---|---|
3 radiometers in push-broom alignment |
|
Scatterometer |
|
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
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
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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