The National Aeronautics and Space Administration (NASA) Soil Moisture Active Passive (SMAP) satellite was launched in January 2015. In order to validate the soil moisture retrieval algorithms that fully exploit the unique capabilities of SMAP, the algorithms need to be tested over different conditions worldwide. In response to this need, the Terrestrial Hydrology Experiment 2018 in Mexico (THEx-MEX 18) was conducted in Huamantla, Tlaxcala, Mexico over a six-month period. Ground crews collected soil moisture data, crop measurements, and biomass samples in support of this campaign. The objective of THEx-MEX was to create a soil moisture network over an agricultural area in Mexico, understand the spatial distribution of soil moisture, and compare the SMAP soil moisture retrievals with in-situ measurements. This work details the field data collection as well as data calibration and analysis. A first comparison between in-situ data and SMAP retrievals of soil moisture is presented. It is demonstrated that absolute soil moisture values can be delivered by satellite observations. SMAP soil moisture estimates closely follow dry down and wetting events observed during the field experiment.

Project Objectives

Estimation of Biophysical Variables

Operational Implementation Plan

This file describes the protocols implemented to characterize the soil and vegetation conditions.


Biophysical Variables
  • fAPAR (Fraction of Absorbed Photosynthetically Active Radiation)
  • LAI (Leaf Area Index)
  • Biomass
  • fCover
  • Plant height

Site Description

Landscape TopographyValley
Typical Field Size5 fields of about 6300 m^2
Climatic ZoneTropics, warm
Major Crops and Calendars

Maize (Early,Normal,Late):
Calendar: April - October
Typical Rotation: In general, there is not crop rotation in these fields.

Soil Type & Texture


  • Sand
  • Silt
  • Clay
Soil Drainage Class
Irrigation InfrastructureRainfed fields
Other Site Details

The agricultural fields are located in Huamantla, Central Mexico (19º 18’ 51.09’’ N; 97º 51’ 27.91’’W). Huamantla is a small city in Huamantla Municipality located in the eastern half of the Mexican state of Tlaxcala. The municipality’s economy is still heavily agricultural, with almost a third of its workforce dedicated to crops and livestock. Over half of the municipality’s territory is used for farming and grazing but agriculture’s role has been diminishing. In 2009, the municipality had 24,424 hectares under cultivation with crops such as corn, beans, wheat, animal feed, peaches and rye. Livestock includes cattle (mostly dairy), pigs, sheep, goats and domestic fowl. The climate of Huamantla is characteristically temperate (subhumid). Rainfall occurs from May to October, ranging from 500 mm per year East to 800-1000 mm in the Southwest. Rainfall variations in the mid-summer months can lead to extended droughts. Average monthly temperatures fluctuate within a narrow range, with January being the coldest month (0-9 ºC) and April or May generally the warmest (19-27 ºC). Huamantla soils are generally sandy and highly drained, though some soils are gravelly or rocky. Depth varies from 10 cm in the Lithosols of the west and north central regions to deep Fluviols on the plains of Huamantla.

In Situ Observations

Biomass, geometric description, soil moisture, soil texture, surface roughness

  • Crop Type(s): Maize
  • Collection Protocol:

    The protocols implemented are described in the following file:


  • Frequency: Every three weeks over six months

EO Data

Optical Data Requirements

SAR Data Requirements

Passive Microwave Data Requirements

Thermal Data Requirements

Project Reports

Study Team

Team Leader

  • Name: Aljeandro Monsivais-Huertero
  • Affiliation: Insituto Politecnico Nacional, Mexico
  • Affiliation Webpage:
  • Position: Full professor
  • Email:
  • Personal Webpage:
  • Phone number: +5215540205330
  • Postal Address: Escuela Superior de Ingeniería Mecánica y Eléctrica Unidad Ticomán. Insituto Politécnico Nacional.
    Calzada Ticomán 600, Colonia San José Ticoman, Delegación Gustavo A. Madero.
    Mexico City. Z.P. 07340.
  • Other Team Members

  • Name: José Carlos Jiménez-Escalona
  • Affiliation: Insituto Politecnico Nacional, Mexico
  • Affiliation Webpage:
  • Position: Full professor
  • Email:
  • Personal Webpage:
  • Role: Co-Lead
  • Name: Eduardo Arizmendi-Vasconcelos
  • Affiliation: Instituto Politécnico Nacional
  • Affiliation Webpage:
  • Position: Master student
  • Email:
  • Personal Webpage:
  • Role: Member
  • Name: Daniel Enrique Constantino-Recillas
  • Affiliation: Instituto Politécnico Nacional
  • Affiliation Webpage:
  • Position: PhD student
  • Email:
  • Personal Webpage:
  • Role: Member