PROGRAMS LPRM_L3_to_obs.f90 AMSR_E_L2_to_obs.f90

This is a brief description of the converters and utilities in this directory retrieved from the NASA Earthdata portal This is a front end for many (Distributed Active Archive Center) DAAC portals and for the Goddard Earth Sciences Data and Information Services Center

These directories contain satellite retrieval data for land surface soil moisture and leaf area index (LAI).

The general workflow for each of the observation converters (described in more detail below) is usually:

  1. Download the data for the period in question (see DATA SOURCES below)

  2. Build the DART executables with support for the soil moisture observations. This is done by running preprocess with obs_def_land_mod.f90 in the list of input_files for preprocess_nml.

  3. Convert each data file individually (e.g. executing LPRM_L3_to_obs)

  4. Combine or subset all output files for the region and timeframe of interest into one file using program obs_sequence_tool

For some models (CLM, for example), it is required to reorganize the observation sequence files into a series of files that contains ONLY the observations for each assimilation. This can be achieved with the ~/models/clm/shell_scripts/makedaily.sh script. Since there are subtleties for each model, makedaily.sh is generally found in the shell_scripts directory of the model.

Soil Moisture Observation Converters

Program AMSR_E_L2_to_obs.f90

Description

AMSR-E/Aqua surface soil moisture (LPRM) L2B V002 is a Level 2 (swath) data set. Its land surface parameters, surface soil moisture, land surface (skin) temperature, and vegetation water content are derived from passive microwave remote sensing data from the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E), using the Land Parameter Retrieval Model (LPRM). Each swath is packaged with associated geolocation fields. The data set covers the period from June 2002 to October 2011 (when the AMSR-E on the NASA EOS Aqua satellite stopped producing data due to a problem with the rotation of its antenna), at the spatial resolution (nominally 56 and 38 km, respectively) of AMSR-E’s C and X bands (6.9 and 10.7 GHz, respectively).

NAMELIST

This namelist is read from the file input.nml. Namelists start with an ampersand ‘&’ and terminate with a slash ‘/’. Character strings that contain a ‘/’ must be enclosed in quotes to prevent them from prematurely terminating the namelist.

&AMSRE_L2_to_obs_nml
   input_file          = 'LPRM-AMSR_E_L2_D_SOILM2_V002_20030630025503.nc'
   obs_out_file        = 'obs_seq.out'
   max_rfi_code        = 2
   amsre_rep_error     = 2
   /

Description of namelist variables:

Contents

Type

Description

input_file

character(len=256)

Name of the netcdf soil moisture data file.

obs_out_file

character(len=256)

Name of the output observation sequence file.

max_rfi_code

integer

Maximum Radio Frequency Interference. Soil moisture values with a max rfi above this threshold are excluded from obs_out_file

amsre_rep_error

integer

Representativeness Error (standard deviation units). This value is added to the instrument error provided from the input file to calculate the total observation error variance

Important

The total error (instrument error + representativeness error) is used to calculate the observation error variance in the obs_out_file. The instrument error is taken from the data file variable (sm_c_error or sm_x_error), whereas the represenativeness error (amsre_rep_error) is a namelist variable input by the user at runtime.

Data Source

The dataset (LPRM_AMSRE_SOILM2: AMSR-E/Aqua surface soil moisture (LPRM) L2B V002) can be found here.

Program LPRM_L3_to_obs.f90

Description

TMI/TRMM surface soil moisture (LPRM) L3 1 day 25 km x 25 km nighttime V001 is Level 3 (gridded) data set. Its land surface parameters, surface soil moisture, land surface (skin) temperature, and vegetation water content, are derived from passive microwave remote sensing data from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI), using the Land Parameter Retrieval Model (LPRM). There are two files per day, one daytime and one nighttime, archived as two different products. This document is for the nighttime product. The data set covers the period from December 1997 to April 2015 (when the instruments on the TRMM satellite were shut down in preparation for its reentry into the earth’s atmosphere).

The LPRM is based on a forward radiative transfer model to retrieve surface soil moisture and vegetation optical depth. The land surface temperature is derived separately from TMI’s Ka-band (37 GHz). A unique feature of this method is that it can be applied at any microwave frequency, making it very suitable to exploit all the available passive microwave data from various satellites.

NAMELIST

This namelist is read from the file input.nml. Namelists start with an ampersand ‘&’ and terminate with a slash ‘/’. Character strings that contain a ‘/’ must be enclosed in quotes to prevent them from prematurely terminating the namelist.

&LPRM_L3_to_obs_nml
   input_file        = 'LPRM-TMI_L3_NT_SOILM3_V001-20120411T144345Z_20120407.nc'
   output_file       = 'obs_seq.out'
   lon_bounds        = 0.0, 360.0
   lat_bounds        = -90.0,  90.0
   /

Description of namelist variables:

Contents

Type

Description

input_file

character(len=256)

Name of the netcdf soil moisture data file.

output_file

character(len=256)

Name of the output observation sequence file.

lon_bounds

real(r8)

Longitude bounds. Observations outside these bounds are excluded from the output_file

lat_bounds

real(r8)

Latitude bounds. Observations outside these bounds are excluded from the output_file

Important

The total error (instrument error + representativeness error) is used to calculate the observation error variance in the output_file. The instrument error is taken from the data file variable (sm_x_error), whereas the representativeness error is set to 0.1 within the LPRM_L3_to_obs.

Data Source

The dataset (LPRM_TMI_NT_SOILM3: TMI/TRMM surface soil moisture (LPRM) L3 1 day 25km x 25km nighttime V001) can be found here.

Leaf Area Index Observation Converter

Program netCDF_to_obs.f90

Description

This dataset provides a global 0.25 degree x 0.25 degree gridded monthly mean leaf area index (LAI) climatology as averaged over the period from August 1981 to August 2015. The data were derived from the Advanced Very High Resolution Radiometer (AVHRR) Global Inventory Modeling and Mapping Studies (GIMMS) LAI3g version 2, a bi-weekly data product from 1981 to 2015 (GIMMS-LAI3g version 2). The LAI3g version 2 (raw) data were first regridded from 1/12 x 1/12 degree to 0.25 x 0.25 degree resolution, then processed to remove missing and unreasonable values, scaled to obtain LAI values, and the bi-weekly LAI values were averaged for every month. Finally, the monthly long-term mean LAI (1981-2015) was calculated.

The Global Monthly Mean Leaf Area Index Climatology, (1981-2015) dataset may be converted with the netCDF_to_obs program. Since these are monthly means, each timestep is read and output as their own observation sequence file that has the date and time appended to the filename.

NAMELIST

&netCDF_to_obs_nml
   input_file        = 'LAI_mean_monthly_1981-2015.nc4'
   output_file_base  = 'obs_seq.out'
   lon_bounds        = 0.0, 360.0
   lat_bounds        = -90.0,  90.0
   debug               = .FALSE.
   observation_varname          = 'LAI'
   observation_type             = 'GIMMS_LEAF_AREA_INDEX'
   obs_error_standard_deviation = 0.2
   /

Description of namelist variables:

Contents

Type

Description

input_file

character(len=256)

Name of the netcdf LAI data file.

output_file_base

character(len=256)

Name of the output observation sequence file.

lon_bounds

real(r8)

Longitude bounds. Observations outside these bounds are excluded from the output file

lat_bounds

real(r8)

Latitude bounds. Observations outside these bounds are excluded from the output file

debug

logical

If .TRUE. prints out extra information on data file characteristics

observation_varname

character(len=256)

Name of of the leaf area variable within the netcdf data file

observation_type

character(len=256)

Name of the DART observation type

obs_error_standard_deviation

character(len=256)

The observation error standard deviation (not provided within data file)

Data Source

The Global Monthly Mean Leaf Area Index Climatology, (1981-2015) data can be found here.