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Fast All-season Soil STrength Model

Published Feb. 1, 2013


The one-dimensional dynamic state-of-the-ground model FASST (Fast All-season Soil STrength) was developed by researchers at the Engineer Research and Development Center’s Cold Regions Research and Engineering Laboratory (ERDC-CRREL) as part of the Army’s Battlespace Terrain Reasoning and Awareness research program. FASST calculates the ground’s moisture and/or ice content, temperature, and freeze/thaw profiles, as well as soil strength and surface ice and snow accumulation/depletion. FASST’s fundamental operations are the calculation of an energy and water budget that quantifies both the flow of heat and moisture within the soil and also the exchange of heat and moisture at all interfaces (ground/air or ground/snow; snow/air) using both meteorological and terrain data.

FASST is designed to accommodate a range of users, from those having intricate knowledge of a site to those knowing only the site location. It allows for 22 different terrain materials, including asphalt, concrete, bedrock, permanent snow, and Unified Soil Classification System (USCS) soil types. At a minimum, the only weather information required is air temperature. The code is written in FORTRAN95 and is publicly available.


The ability to predict the state of the ground is essential to manned and unmanned vehicle mobility and personnel movement, and to determine sensor performance for military and civilian activities. Trafficability, or ease of travel, is dictated by both soil strength and surface friction, and decreases in the presence of an ice or snow layer or when the top of the ground becomes too wet. Soil strength depends on soil type and on the distribution of
water and ice with depth, e.g., the presence of a thawed layer (wet, low bearing capacity) overlying a competent layer of frozen ground has a negative impact on mobility as motion resistance increases and traction decreases. Because infrared and radar sensor performance is determined, in part, by state of the ground, weather-impacted state-of-the-ground conditions resulting in a high degree of clutter can degrade sensor performance.

Expected Cost to Implement

FASST is free to anyone.


FASST is validated, flexible, and easy to use. It is used by military and civilian programs and has been exercised over a range of global latitudes that experience winter conditions. Researchers at Colorado State University have used FASST to investigate soil moisture and snow accumulation/depletion and sensor performance studies carried out at the Naval Postgraduate School, AER (Atmospheric and Environmental Research, Inc.), and ERDC-CRREL. FASST also is included in the military version of ESRI’s Arc/Info, Commercial Joint Mapping Tool Kit, and the Army’s Digital Topographic Support System.


In its original form, the only effects vegetation had on FASST were to change surface albedo and emissivity, both of which alter the soil surface energy and moisture budgets. A two-tier, multi-layer vegetation algorithm has been added that can be implemented separately or jointly.

Distribution Sources

  • How to get FASST.doc (a good place to start; explains what is where and basic file functions)
  • fasst_user_document.doc (main FASST user’s documentation, updated as necessary)
  • SR-04-1.pdf (main technical documentation)TR-04-25.pdf (vegetation modules technical documentation)
  • TR-08-7.pdf (describes upgrades made to original code)

The other 5 zip files contain:

  •  fasst.sf3 (change name to fasst.exe – runs FASST)
  •  make files (unix compatible, 1 for PGI and 1 for Absoft; Mac OS X lion, for GNU )
  •  FORTRAN95 source code (thirty files)
  •  fasstusersoil.inp (file containing user-specified soil information)
  •  FASST_defaultlayerprop.inp (contains all default soil properties used by FASST)
  •  gr1.inp, test_frqcytable.inp (sample input files)
  •  gr1_soil.inp (gr1 specific soil information)
  •  SingleCellExample_met.out, 2008111006_37N126E_38N128E_sfc.met (met files) 
  • fasst.out, 2008111006_37N126E_38N128E_sfc.fst; ground.out; fluxes.out; snow_info.out; veg_temp.out (sample output files)

  • met_reader.sf3 (change name to met_reader.sf3 – runs the met data processor)
  • make files (unix compatible, 1 for PGI and 1 for Absoft; Mac OS X lion, for GNU)
  • FORTRAN95 source code (six files)
  • weather_single.inp, weather_multi.inp (sample input files for met_reader.exe)
  • SingleCellExample.mta, MultCellExample.mta (sample meta file)
  • SingleCellExample.met, MultCellExample.met (met files associated with mta files)
  • SingleCellExample_met.out, MultCellExample_met.out (output files)
  • met_inferred_single.out, met_inferred_multi.out (log files)

  • bld_met_mta.exe (creates the met data meta file)
  • bld_met_mta.f (FORTRAN source code)
  • SingleCellExample.mta, MultCellExample.mta (sample meta file)
  • SingleCellExample.met, MultCellExample.met (met files associated with mta files)

  • US_soil_tools.exe (creates a user’s soil properties file such as gr1_soil.inp)
  • US_soil_tools.f (FORTRAN source code)

  • read_grout.exe (pulls specific depth information from FASST output ground.out)
  • read_grout.f (FORTRAN source code)


Available Training

Training is not available.


Contact Us, Ph.D., 603.646.4812
Terrestrial & Cryospheric Sciences Branch (CEERD-RR-G)
US Army Engineer Research and Development Center / Cold Regions Research and Engineering Laboratory
Updated 25 August 2020