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This document covers five data sets derived from the NASA Aquarius passive microwave instrument on the Satélite de Aplicaciones Científicas (SAC-D):
We kindly request that you cite the use of this data set in a publication using the following citation example. For more information, see our Use and Copyright Web page.
Bindlish, Rajat and Thomas Jackson. 2013. Aquarius L3 Gridded 1-Degree Daily Soil Moisture, Version 2, [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. http://dx.doi.org/10.5067/Aquarius/AQ3_DYSM.002.
Bindlish, Rajat and Thomas Jackson. 2013. Aquarius L3 Gridded 1-Degree Weekly Soil Moisture, Version 2, [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. http://dx.doi.org/10.5067/Aquarius/AQ3_WKSM.002.
Bindlish, Rajat and Thomas Jackson. 2013. Aquarius L3 Gridded 1-Degree Monthly Soil Moisture, Version 2, [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. http://dx.doi.org/10.5067/Aquarius/AQ3_MOSM.002.
Bindlish, Rajat and Thomas Jackson. 2013. Aquarius L3 Gridded 1-Degree Seasonal Soil Moisture, Version 2, [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. http://dx.doi.org/10.5067/Aquarius/AQ3_SNSM.002.
Bindlish, Rajat and Thomas Jackson. 2013. Aquarius L3 Gridded 1-Degree Annual Soil Moisture, Version 2, [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. http://dx.doi.org/10.5067/Aquarius/AQ3_ANSM.002.
25 August 2011 to present
Daily, Weekly, Monthly, Seasonal, Annual
V2. See the Version History section of this document for previous version information.
Rajat Bindlish and Thomas Jackson
United States Department of Agriculture
Agricultural Research Service
Hydrology and Remote Sensing Laboratory
Beltsville, MD 20705 USA
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
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.
The Aquarius L3 Gridded 1-Degree Soil Moisture data are produced by NASA Goddard Space Flight Center's Ocean Data Processing System (ODPS).
The weekly data start from August 20, 2011 in 7 day duration until the present. The first weekly data have a time period of August 20 to August 26, 2011. Note: Although the weekly periods start from August 20, 2011 there is no Aquarius data before August 25, 2011.
The monthly data for August 2011 is comprised of observations from August 25 to August 31, 2011. The month data for August 2011 is a partial coverage only. Similarly, the yearly data for 2011 has observations after August 25, 2011 only. Therefore, the yearly 2011 data does not cover observations from the entire calendar year of 2011.
The data files are in Hierarchical Data Format 5 (HDF5). The values can be stored as bytes, 2-byte integers, or 4-byte floats. Soil moisture data are 32-bit float, palette is 8-bit unsigned integer. The first two are scaled real values and may be converted to geophysical values using the global attributes Scaling, Scaling Equation, Base, Slope, and Intercept.
Data files are organized into directories by time period, Annual, Daily, Monthly, Seasonal, and Weekly, and within time periods organized by date:
File names correspond to those of their parent Aquarius binned data products, indicating the binning periods as part of the names.
Soil moisture files are named according to the following conventions and as described in Table 1:
|Q||Indicates Aquarius instrument|
|ddd||UTC day of year|
|hhmmsss||UTC hours, minutes, and seconds of the first sample block in the product "Sample block" is defined as the first set of observations from the three Aquarius beams.|
Binning period length, where:
|ppppp||Geophysical parameter: SOILM = soil moisture|
|vvvv||Data version, example: V2.0|
|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 262 KB each.
Spatial coverage is global.
Spatial resolution of the L3 data is 1 degree.
The l2m_data object is a two-dimensional array (180 rows, 360 columns) of an Equidistant Cylindrical (also known as Plate Carrée) projection of the globe.
25 August 2011 to present.
Aquarius/SAC-D data are acquired daily. Aquarius L3 daily, weekly, and monthly soil moisture products are delivered monthly, typically within the month following data acquisition. Aquarius L3 seasonal and annual soil moisture products are delivered seasonally and annually, respectively.
Daily, Weekly, Monthly, Seasonal, and Annual
The weekly periods start from August 20, 2011 to August 26, 2011. The file name specifies the start date and end dates for Aquarius coverage. For example, the weekly file named: Q20120012012007.L3m_7D_SOILM_V2.0_rad_sm_1deg contains data from Day Of Year (DOY) 1, 2012 to DOY 7, 2012.
The seasons are defined between equinox and solstice. The file names contain the exact DOY for each season (Autumn: March 21 to June 21; Summer: June 22 to September 22; Fall: September 23 to December 21; and Winter: December 21 to March 20). For example: the file Q20121732012264.L3m_SNSU_SOILM_V2.0_rad_sm_1deg contains the data for summer 2012 ranging from DOY 173 (June 22, 2012) to DOY 264 (September 22, 2012).
The Level-3 standard mapped image (SMI) products are representations of binned data products generated from Aquarius data. The data object, l3m_data, represents a mean Soil Moisture at each grid point. The grid resolution is 1 degree.
Each Level-3 soil moisture product contains the l3m_data object, with attributes described in Table 2.
|Scaling Equation||(Slope*l3m_data) + Intercept = Parameter value|
The palette object included in the data file is the color palette used in the graphics generated from the mapped files. The user can either use this palette or any palette of their choice.
NetCDF metadata are included as global attributes with the Level-3 data files, as described in Table 3.
|Title||Level-3 Standard Mapped Image|
|Mission Characteristics||Nominal orbit inclination=98.0 (Sun-synchronous) node=6PM (ascending) eccentricity=<0.002 altitude=657 km ground speed=6.825 km/sec|
|Processing Control||smigen par=Q20130012013031.L3m_MO_SOILM_V2.0_rad_sm_1deg.param|
|Input Parameters||IFILE = /data3/sdpsoper/vdc/vpu10/workbuf/Q20130012013031.L3b_MO_SOILM_V2.0.main|OFILE = Q20130012013031.L3m_MO_SOILM_V2.0_rad_sm_1deg|PFILE = |PROD = rad_sm|PALFILE = DEFAULT|PROCESSING VERSION = V2.0|MEAS = 1|STYPE = 0|DATAMIN = 0.000000|DATAMAX = 0.000000|LONWEST = -180.000000|LONEAST = 180.000000|LATSOUTH = -90.000000|LATNORTH = 90.000000|RESOLUTION = 1deg|PROJECTION = RECT|GAP_FILL = 0|SEAM_LON = -180.000000|PRECISION=F|
|L2 Flag Names||0B|
|Period Start Year||0S|
|Period Start Day||0S|
|Period End Year||0S|
|Period End Day||0S|
|Map Projection||Equidistant Cylindrical|
|Latitude Units||degrees North|
|Longitude Units||degrees East|
|SW Point Latitude||-89.5f|
|SW Point Longitude||-179.5f|
|Number of Lines||180|
|Number of Columns||360|
|Scaling Equation||(Slope*l3m_data) + Intercept = Parameter value|
|Suggested Image Scaling Minimum||0.0f|
|Suggested Image Scaling Maximum||0.4f|
|Suggested Image Scaling Type||LINEAR|
|Suggested Image Scaling Applied||No|
Below is a sample of the l3m_data soil moisture data array from the Level-3 Aquarius soil moisture file: Q20130012013031.L3m_MO_SOILM_V2.0_rad_sm_1deg.
Figure 1 shows the average soil moisture estimates for the month of July 2012.
Figure 1. Aquarius soil moisture estimates using all three beams for the month of July 2012.
See the NSIDC Aquarius Soil Moisture Order Data page for a list of order options.
HDF 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 datasets.
For additional tools, see the HDF-EOS Tools and Information Center.
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.
An Aquarius Level-3 Soil Moisture product is generated from physical measurements computed from the Aquarius Level-2 Soil Moisture product. Each Level-3 product contains data from one time period (daily, weekly, monthly, seasonally or yearly) of Aquarius data. 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 Level-3 science file.
The Aquarius Level-3 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 Level-3 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.
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.
V2.0 is the first version of Aquarius Level-3 Soil Moisture data available from NSIDC. Previous versions are available via the NASA Aquarius Web site (http://aquarius.nasa.gov/).
The current Version 2.0 Aquarius calibration is valid over a narrow range of TB (oceans only) (Piepmeier et al. 2013). The Aquarius brightness temperatures are re-calibrated for each beam using co-located and concurrent Soil Moisture Ocean Salinity (SMOS) observations. The re-calibrated brightness temperatures are used in version 2.0 of the soil moisture algorithm. The Aquarius mission is planning to address the full range calibration in the next couple of data releases. These calibration coefficients will be evaluated after each Aquarius data release.
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 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.
|3 radiometers in push-broom alignment||
SAC-D spacecraft Orbit Parameters:
Bindlish, Rajat, and Thomas J. Jackson. 2013. Aquarius Soil Moisture ATBD Users Guide, Version 2.0. Beltsville, Maryland USA: USDA Hydrology and Remote Sensing Lab. (PDF file, 315 KB)
Bindlish, Rajat, Thomas Jackson, Michael Cosh, Tianjie Zhao and Peggy O'Neill. 2013. Global Soil Moisture from the Aquarius Satellite: Description and Initial Assessment. IEEE Geosciences and Remote Sensing Letters (in review).
Lilly, Jonathan and Gary Lagerloef. 2008. Aquarius Level 3 Processing Algorithm Theoretical Basis Document. ftp://podaac-ftp.jpl.nasa.gov/allData/aquarius/docs/v2/AquariusLevel3_GriddingSmoothingPaper_Lilly&Lagerloef2008.pdf
Piepmeier, Jeffrey, Shannon Brown, Joel Gales, Liang Hong, Gary Lagerloef, David Le Vine, Paolo de Matthaeis, Thomas Meissner, Rajat Bindlish, and Thomas Jackson. 2013. Aquarius Radiometer Post-Launch Calibration for Product Version 2.0, Aquarius Project Document: AQ-014-PS-0015. ftp://podaac-ftp.jpl.nasa.gov/allData/aquarius/docs/v2/AQ-014-PS-0015_AquariusInstrumentCalibratrionDescriptionDocument.pdf.
The acronyms used in this document are listed in Table 5.
|ACS||Attitude Control System|
|ADPS||Aquarius Data Processing System|
|ATBD||Algorithm Theoretical Basis Document|
|CONAE||Comisión Nacional de Actividades Espaciales|
|GPS||Global Positioning System|
|GSFC||Goddard Space Flight Center|
|HDF5||Hierarchical Data Format 5|
|HH||transmit Horizontal, receive Horizontal|
|HV||transmit Horizontal, receive Vertical|
|IGBP||International Geosphere-Biosphere Programme|
|MODIS||Moderate Resolution Imaging Spectroradiometer|
|NASA||National Aeronautics and Space Administration|
|NCEP GFS||National Centers for Environmental Prediction Global Forecast System|
|NCEP GFS GDAS||National Centers for Environmental Prediction Global Forecast System Global Data Assimilation System|
|NDVI||Normalized Difference Vegetation Index|
|NOAA||National Oceanic and Atmospheric Administration|
|NRCS||Normalized Radar Cross Section|
|ODPS||Ocean Data Processing System (ODPS)|
|OISST||Optimum Interpolation (OI) Sea Surface Temperature (SST) V2|
|RFI||Radio Frequency Interference|
|SAC-D||Satélite de Aplicaciones Científicas|
|SCA||Single Channel Algorithm|
|SeaWiFS||Sea-viewing Wide Field-of-view Sensor|
|SMOS||Soil Moisture Ocean Salinity|
|SWE||Snow Water Equivalent|
|TOA||Top Of Atmosphere|
|UTC||Coordinated Universal Time|
|VH||transmit Vertical, receive Horizontal)|
|VV||transmit Vertical, receive Vertical)|
|VWC||Vegetation Water Content|
02 December 2013
03 June 2014