exposure times, and the lack of long time series and
exposure times, and the lack of long time series and
continuous records at all stations, are some of the
continuous records at all stations, are some of the
other problems with weather station data. This data is
other problems with weather station data. This data is
therefore not always available and has limited spatial
therefore not always available and has limited spatial
coverage.
coverage.
The introduction of satellites has made it possible to
The introduction of satellites has made it possible to
measure the temperature of the Earth’s surface over
measure the temperature of the Earth’s surface over
large areas. These data are nearly always available
large areas. These data are nearly always available
and have extensive spatial coverage in contrast with
and have extensive spatial coverage in contrast with
air temperature measurements that are limited to
air temperature measurements that are limited to
weather stations.
weather stations.
Using surface temperature measured by satellites (Ts)
Using surface temperature measured by satellites (Ts)
to estimate air temperature (Ta) is therefore an
to estimate air temperature (Ta) is therefore an
ongoing focus of research in climate change studies
ongoing focus of research in climate change studies
[1][9][10][11]. There are differences between the two
[1][9][10][11]. There are differences between the two
variables. Surface temperature is highly dependent on
variables. Surface temperature is highly dependent on
the surface type and changes rapidly in space and
the surface type and changes rapidly in space and
time as the surface heats and cools in response to
time as the surface heats and cools in response to
solar radiation. The air temperature shows more
solar radiation. The air temperature shows more
stability and, although measured at a fixed point,
stability and, although measured at a fixed point,
could be argued to be representative of the local mean
could be argued to be representative of the local mean
temperature.
temperature.
To model the non-linear and complex relationship
To model the non-linear and complex relationship
between Ta and Ts, machine learning algorithms are a
between Ta and Ts, machine learning algorithms are a
promising option compared with other statistical
promising option compared with other statistical
methods and are investigated in this paper. The next
methods and are investigated in this paper. The next
sections will cover past studies, methodology, data
sections will cover past studies, methodology, data
collection, data analysis, results and conclusions.
collection, data analysis, results and conclusions.
2
2Past Studies
Past Studies
2.1
2.1 Climate Change
Climate Change
There have been many attempts to derive air
There have been many attempts to derive air
temperature from the surface temperature in different
temperature from the surface temperature in different
environments. These include [9] in the Arctic, [10] in
environments. These include [9] in the Arctic, [10] in
Canada and Alaska, [11] in Russia and China, [4] on
Canada and Alaska, [11] in Russia and China, [4] on
the Tibetan Plateau in western China, [5] in Portugal,
the Tibetan Plateau in western China, [5] in Portugal,
[1] and [6] in Africa. Not all of these have specifically
[1] and [6] in Africa. Not all of these have specifically
focused on high mountain environments where the
focused on high mountain environments where the
difference between air and surface temperature can
difference between air and surface temperature can
become instantaneously large due to intense radiation
become instantaneously large due to intense radiation
at high elevations. They also cover a wide range of
at high elevations. They also cover a wide range of
different vegetation zones including forests, deserts
different vegetation zones including forests, deserts
and snow covered landscapes. In all cases it is most
and snow covered landscapes. In all cases it is most
common to build regression models to estimate air
common to build regression models to estimate air
temperature from surface temperature. Although
temperature from surface temperature. Although
regression models are a solid framework for modeling
regression models are a solid framework for modeling
and have been widely applied in the references above,
and have been widely applied in the references above,
the introduction of new machine learning algorithms
the introduction of new machine learning algorithms
to the research environment in recent years presents
to the research environment in recent years presents
an alternative approach that needs to be evaluated.
an alternative approach that needs to be evaluated.
2.2
2.2 Machine Learning
Machine Learning
The application of machine learning algorithms in
The application of machine learning algorithms in
climate science and weather forecasting goes back to
climate science and weather forecasting goes back to
the works of [12] and [13] who investigated the
the works of [12] and [13] who investigated the
application of Expert Systems (ES) and Artificial
application of Expert Systems (ES) and Artificial
Neural Network (ANN) respectively.
Neural Network (ANN) respectively.
Machine learning has also been applied to the
Machine learning has also been applied to the
prediction of air temperature from surface
prediction of air temperature from surface
temperature but in a limited way. The research papers
temperature but in a limited way. The research papers
[14], [15], [16], [17], and [18] all use ANN (Artificial
[14], [15], [16], [17], and [18] all use ANN (Artificial
Neural Networks) for this purpose. However, other
Neural Networks) for this purpose. However, other
machine learning algorithms including ANFIS
machine learning algorithms including ANFIS
(Adaptive Neuro Fuzzy Systems) have been so far
(Adaptive Neuro Fuzzy Systems) have been so far
restricted to weather forecasting
restricted to weather forecasting
applications and have
applications and have
not been used to estimate air temperature from surface
not been used to estimate air temperature from surface
temperature in a climate context. These past research
temperature in a climate context. These past research
examples also commonly used variable types other
examples also commonly used variable types other
than Ta and Ts to estimate air temperature. The
than Ta and Ts to estimate air temperature. The
combination of a wide variety of machine learning
combination of a wide variety of machine learning
algorithms with the core variables could present a
algorithms with the core variables could present a
simple but equally efficient approach to the
simple but equally efficient approach to the
estimation of air temperature from surface
estimation of air temperature from surface
temperature.
temperature.
2.3
2.3 Summary
Summary
Past research on the application of machine learning
Past research on the application of machine learning
algorithms in the estimation of air temperature is
algorithms in the estimation of air temperature is
limited to a few algorithms. This research therefore
limited to a few algorithms. This research therefore
will evaluate the application of several machine
will evaluate the application of several machine
learning algorithms using only the two core variables,
learning algorithms using only the two core variables,
namely surface temperature (Ts) and air temperature
namely surface temperature (Ts) and air temperature
(Ta) to present a novel and simple but efficient
(Ta) to present a novel and simple but efficient
approach to the estimation of air temperature from
approach to the estimation of air temperature from
surface temperature.
surface temperature.
3
3Research Methodology
Research Methodology
Modeling of large scale, complex, non-linear, ill-
Modeling of large scale, complex, non-linear, ill-
defined, and uncertain systems such as climate change
defined, and uncertain systems such as climate change
systems has been a prime concern for a long time.
systems has been a prime concern for a long time.
The application of machine learning (ML) algorithms
The application of machine learning (ML) algorithms
such as fuzzy systems and neural networks have
such as fuzzy systems and neural networks have
opened a path for more ML algorithms to be tested
opened a path for more ML algorithms to be tested
and used in this field. Five main algorithms were
and used in this field. Five main algorithms were
employed in this study (described below).
employed in this study (described below).
3.
3.1
1 ANFIS (Adaptive Neuro Fuzzy System)
ANFIS (Adaptive Neuro Fuzzy System)
ANFIS is an implementation of a FIS (Fuzzy
ANFIS is an implementation of a FIS (Fuzzy
Inference System) on top of the architecture of an
Inference System) on top of the architecture of an
ANN (Artificial Neural Network) combining the
ANN (Artificial Neural Network) combining the
power of a fuzzy rule base with the learning
power of a fuzzy rule base with the learning
capability of neural networks. For a discussion see
capability of neural networks. For a discussion see
[19].
[19].