THERMAL INERTIA MODELLING FOR SOIL MOISTURE ASSESSMENT
BASED ON REMOTELY SENSED DATA.
Beata Hejmanowska, research assistant, University of Mining and Metallurgy, Cracow, Poland
Stanistaw C. Mularz, senior lecturer, University of Mining and Metallurgy, Cracow, Poland
Commission VII, Working Group 1
KEY WORDS: Remote Sensing, Soil, Thermal, Surface, Model, Remote Sensing Soil Mapping, Thermal Inertia
Modelling, Soil moisture assessment.
ABSTRACT
After Pratt's. et al. (1980) the thermal inertia model have been used for soil moisture assessment of the bare soil sur-
face. As an input data the model requires the digital images of soil albedo (A), diurnal temperature differences (AT) and
also a set of geographical / meteorological data. For the study area (4 x 4 km) the data were collected during the two-
level experiment consisted of an airborne remote sensing imagery and the simultaneously in situ measurements. After
calibration procedure of the remotely sensed data the maps of thermal inertia and soil-moisture distribution on the test
fields were generated. A good approach to the different data categories was achieved. A removal of the topographical
effect using Digital Elevation Model (DEM) ofthe study area and Lambert's method was also tested.
1. INTRODUCTION — Series of airborne thermal images which correspond-
ing to the maximum and the minimum diurnal tem-
A suitable method for remote measurements of soil perature,
moisture is not elaborated as yet. It seems, on the base of — data of in situ monitoring the soil temperature and
the literature, that the suitable part of a spectrum for reg- water content,
istration of a wet soil is thermal infrared. In the future it _ terrestrial thermal imagery of the selected part of the
will be probably possible to use a microwave, but till now test area.
the property of this part of spectrum has not fully recog- Example of topographical correction and its influence on
nized for this purpose. The best method according to the the thermal inertia modeling is also presented. The
soil water assessment using remote sensing data, is method of calibration of the remotely sensed data and the
based on the thermal inertia model. The thermal inertia results of testing of the thermal inertia model using a set
value (P) depends on thermal conductivity (k), heat ca- of the experimental airborne data and real ground obser-
pacity (c) and density (p) of the ground : vation are also described.
P= Jkep The research was conducted within the project of the
The inertia can be calculated using not only this directly Polish Committee of Scientific Research (grant No 9 S605
measured soil parameters but also on the base of remote 019 06)
sensing data. For this method it is necessary to know
values of the following remotely measured variables: the
maximum diurnal temperature differences and albedo. 2. STUDY AREA AND DATA COLLECTION
The thermal inertia (P) can be calculated on the base of
this input data using the numerical model taking into The study area is located in the southern part of Poland
account meteorological conditions and geographical co- near the Carpatian Foothills, approximately 50 km east of
ordinates. Theoretical backgrounds of the soil thermal Cracow (Fig.1.). Considering the main purpose of this
inertia model were given by H.S. Carslaw and J.C. Jeager investigation, the two-level experiment was performed in
(1953). Heat conducting within the ground is governed by the early spring-time of 1995 ( 2-3 May ).
the known heat diffusion equation. There are many ways Remotely sensed data were collected over the 4.0 x 4.0
to solve this heat diffusion equation. The results depend km study area within the rural region.
on boundary conditions and a chosen solution method. The airborne panchromatic photos of the study area have
Many authors published own methods of thermal inertia been taken at 2 o'clock p.m. on ILFORD HP5 PLUS film,
modeling. It seems to be, that Pratt D.A. et. al. (1980) using small-frame camera (70 x 56 mm).
proposed the best one. They consider in the energy bal- The thermal infrared (TIR) imageries have been taken
ance the energy provided to the ground (Sun radiation using the AGEMA THERMOVISION SYSTEM 780 which
and sky radiation), and the energy given by the ground on-board registered the series of thermal images in digital
(radiation emitted by ground, sensible heat flux and latent format.
heat flux). For measurement of the maximum diurnal temperature
Estimation of the water content on the bare soil surface differences two thermal flights were done over the study
was the main goal of the study presented. For this pur- area, the first about 2 o'clock p.m. and the second about
pose the airborne / terrestrial experiment was performed. 5 o'clock a.m. just before the sunrise.
The following experimental data set was acquired: 1. The study area consists of several agriculture fields
airborne panchromatic photos of the test area, and the similar soil type - loess and loess-like. The
four fields (A,B,C,D) were selected as the test areas
for the in situ investigations (Fig.1.).
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
