Abstract
Abstract
-Air Temperature is a fundamental measure of the Earth’s climate but is only measured at fixed
-Air Temperature is a fundamental measure of the Earth’s climate but is only measured at fixed
locations. Land surface temperature can be measured widely using satellites. To estimate air temperature (Ta)
locations. Land surface temperature can be measured widely using satellites. To estimate air temperature (Ta)
from the surface temperature (Ts) measured on the forested slopes of Kilimanjaro, four models with unique sets
from the surface temperature (Ts) measured on the forested slopes of Kilimanjaro, four models with unique sets
of inputs were tested using five machine learning algorithms. The RMSE for each model was compared with a
of inputs were tested using five machine learning algorithms. The RMSE for each model was compared with a
benchmark model. Models and algorithms were ranked according to their RMSE (Root Mean Square Error)
benchmark model. Models and algorithms were ranked according to their RMSE (Root Mean Square Error)
The models and algorithms reliability and consistency ranking were calculated. The best model and algorithm
The models and algorithms reliability and consistency ranking were calculated. The best model and algorithm
were determined. Novel models results were compared with the benchmark model. All models outperformed
were determined. Novel models results were compared with the benchmark model. All models outperformed
the benchmark model in the consistency ranking while three out of four models outperformed the benchmark
the benchmark model in the consistency ranking while three out of four models outperformed the benchmark
model in the reliability ranking. Thus machine learning improves the estimation of air temperature in this
model in the reliability ranking. Thus machine learning improves the estimation of air temperature in this
forested environment.
forested environment.
Keywords
Keywords
— Machine learning, air temperature, surface temperature, Kilimanjaro
— Machine learning, air temperature, surface temperature, Kilimanjaro
1
1Introduction
Introduction
Kilimanjaro is the largest and highest free-standing
Kilimanjaro is the largest and highest free-standing
mountain in the world. It lies approximately on the
mountain in the world. It lies approximately on the
equator with a base lying below 1000m and the
equator with a base lying below 1000m and the
summit at 5895m. The landscape is naturally divided
summit at 5895m. The landscape is naturally divided
into several vegetation zones according to elevation.
into several vegetation zones according to elevation.
The forest zone extends from 1800 to 3000 m [1] and
The forest zone extends from 1800 to 3000 m [1] and
is the focus of this study. Other zones on the
is the focus of this study. Other zones on the
mountain (from highest elevations downwards)
mountain (from highest elevations downwards)
include the summit ice-fields, alpine desert,
include the summit ice-fields, alpine desert,
moorland, giant heather, cultivated land and finally
moorland, giant heather, cultivated land and finally
the urban zone. Many of these ecosystems have
the urban zone. Many of these ecosystems have
attracted much attention because of their high impact
attracted much attention because of their high impact
on local and regional climate change.
on local and regional climate change.
The core problem associated with current climate
The core problem associated with current climate
change is the build up of carbon dioxide in the
change is the build up of carbon dioxide in the
atmosphere. Forests play two unrivaled roles in this
atmosphere. Forests play two unrivaled roles in this
respect. First, they remove around 30% of carbon
respect. First, they remove around 30% of carbon
emissions released into the atmosphere due to fossil
emissions released into the atmosphere due to fossil
fuel burning, and second they store large reserves of
fuel burning, and second they store large reserves of
carbon, amounting to double the amount of carbon in
carbon, amounting to double the amount of carbon in
the atmosphere [2].
the atmosphere [2].
Cloud forests such as those on the lower slopes of
Cloud forests such as those on the lower slopes of
Kilimanjaro also play another important role more
Kilimanjaro also play another important role more
locally in encouraging cloud formation, collecting
locally in encouraging cloud formation, collecting
cloud water and distributing it around the local
cloud water and distributing it around the local
watershed, enriching the surrounding ecosystem and
watershed, enriching the surrounding ecosystem and
providing a habitat for rare species [3].
providing a habitat for rare species [3].
Air temperature is one of the most important variables
Air temperature is one of the most important variables
in the quantification of climate change [4][5][6] and
in the quantification of climate change [4][5][6] and
many studies have suggested that mountain regions
many studies have suggested that mountain regions
are warming faster than other locations. This
are warming faster than other locations. This
phenomenon of elevation dependent warming (EDW)
phenomenon of elevation dependent warming (EDW)
has been the subject of much research [4][7][8]. The
has been the subject of much research [4][7][8]. The
increase in air temperature during the past decades
increase in air temperature during the past decades
has not only led to the retreat of glaciers on the upper
has not only led to the retreat of glaciers on the upper
slopes of Kilimanjaro but has also contributed
slopes of Kilimanjaro but has also contributed
towards wild fires that have destroyed nearly one
towards wild fires that have destroyed nearly one
third of Kilimanjaro’s forest cover [3]. Arguably this
third of Kilimanjaro’s forest cover [3]. Arguably this
has a more extensive overall impact on the whole
has a more extensive overall impact on the whole
Kilimanjaro ecosystem than retreating glaciers. This
Kilimanjaro ecosystem than retreating glaciers. This
highlights the importance of obtaining reliable
highlights the importance of obtaining reliable
estimates of air temperature in the forested zone of
estimates of air temperature in the forested zone of
Kilimanjaro.
Kilimanjaro.
The standard method to measure air temperature is
The standard method to measure air temperature is
directly at weather stations at 2m height above the
directly at weather stations at 2m height above the
surface. There are problems with this approach. The
surface. There are problems with this approach. The
measurement is valid only for the precise location of
measurement is valid only for the precise location of
the weather station and not a large area. Mountain
the weather station and not a large area. Mountain
regions in particular are often inaccessible and suffer
regions in particular are often inaccessible and suffer
from a lack of weather stations. The uneven
from a lack of weather stations. The uneven
distribution of stations, changes in instrument
distribution of stations, changes in instrument
Modeling Air Temperature in Forested Areas using Machine Learning
1MASSOUD FOROOSHANI, 1,2ALEXANDER GEGOV, 3NICK PEPIN, 1MO ADDA
1School of Computing The University of Portsmouth, Portsmouth, UK
2English Language Faculty of Engineering, Technical University of Sofia, BULGARIA
3School of the Environment, Geography and Geosciences, The University of Portsmouth, UK
Received: Agust 17, 2021. Revised: April 12, 2022. Accepted: May 9, 2022. Published: June 3, 2022.
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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].
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figure 1: ANFIS architecture [20]
figure 1: ANFIS architecture [20]
3.2 Linear Regression
3.2 Linear Regression
Linear regression is modelling of the relationship
Linear regression is modelling of the relationship
between one or more linear independent variables to
between one or more linear independent variables to
predict a dependent variable. The basic regression
predict a dependent variable. The basic regression
model for one independent variable is in the form of
model for one independent variable is in the form of
yi=β0+β1+Xi+ϵi
(1)[21]
(1)[21]
where
where
yi
is the response variable in the
is the response variable in the
trial
trial
β0
and
and
β1
are parameters
are parameters
Xi
is a known constant (the value of the independent
is a known constant (the value of the independent
variable in the
variable in the
ith
trial)
trial)
ϵi
is a random error
is a random error
β0
and
and
β1
are called regression coefficients.
are called regression coefficients.
β1
is the slope of the regression line.
is the slope of the regression line.
β0
is the Y-intercept of the regression line.
is the Y-intercept of the regression line.
3.3 Polynomial Regression
3.3 Polynomial Regression
Polynomial multiple regression models are special
Polynomial multiple regression models are special
cases of the general linear regression models that can
cases of the general linear regression models that can
have more than one independent variable and
have more than one independent variable and
variables can take various powers. The general form
variables can take various powers. The general form
for one independent variable in second order is:
for one independent variable in second order is:
Yi=β0+β1Xi+β2Xi
2+ϵi
(2)[22]
(2)[22]
3.4 Support Vector Machine
3.4 Support Vector Machine
SVM is one of the most popular ML algorithms,
SVM is one of the most popular ML algorithms,
developed by [22]. It was packaged as LIBSVM
developed by [22]. It was packaged as LIBSVM
library by [23] to make application easier.
library by [23] to make application easier.
figure 2: Support Vector Machine
figure 2: Support Vector Machine [24]
[24]
SVM maps the input vectors into a high dimensional
SVM maps the input vectors into a high dimensional
feature space Z through non-linear mapping chosen a
feature space Z through non-linear mapping chosen a
priori. In this space a linear decision surface is
priori. In this space a linear decision surface is
constructed with special properties that ensures high
constructed with special properties that ensures high
generalization ability of the network.
generalization ability of the network.
3.5 Simple Regression Tree
3.5 Simple Regression Tree
Regression trees are a type of decision tree that
Regression trees are a type of decision tree that
targets continuous variables. This algorithm builds a
targets continuous variables. This algorithm builds a
tree to predict the output from various inputs. In the
tree to predict the output from various inputs. In the
recursive partitioning mode. The space is
recursive partitioning mode. The space is
continuously divided into smaller areas that contain a
continuously divided into smaller areas that contain a
simple model, and therefore the global model has two
simple model, and therefore the global model has two
parts, the recursive partitioning and the simple model.
parts, the recursive partitioning and the simple model.
The regression tree uses a tree to represent the
The regression tree uses a tree to represent the
recursive partitioning in which each cell or terminal
recursive partitioning in which each cell or terminal
node contains a simple model. The model in each
node contains a simple model. The model in each
node is a constant estimate of the output.
node is a constant estimate of the output.
If the points;
If the points;
(
X1,Y 1
)
,
(
X2, Y2
)
,...
(
Xc,Y c
)
are all the
are all the
samples belonging to the leaf-node I. Then the model
samples belonging to the leaf-node I. Then the model
for I is:
for I is:
^
y=1
C
i=1
c
yi
(4)[25]
(4)[25]
4
4Data Collection and Analysis
Data Collection and Analysis
4.1 Data
4.1 Data
The full data-set consists of air and surface
The full data-set consists of air and surface
temperatures recorded at 22 sites across Kilimanjaro
temperatures recorded at 22 sites across Kilimanjaro
between 990 and 5803 m above sea level [26]. It has
between 990 and 5803 m above sea level [26]. It has
been used before by [1] in a preliminary comparison
been used before by [1] in a preliminary comparison
of air and surface temperatures across the mountain.
of air and surface temperatures across the mountain.
In this study four sites within the forest zone were
In this study four sites within the forest zone were
selected, one on the north-ease slope and three on the
selected, one on the north-ease slope and three on the
south-west slope of the mountain. The range of
south-west slope of the mountain. The range of
elevation is from 1890 to 2745m.
elevation is from 1890 to 2745m.
The air temperature (Ta) at each site is recorded using
The air temperature (Ta) at each site is recorded using
an automatic data loggers (Hobo U23-001)
an automatic data loggers (Hobo U23-001)
installed
installed
in a radiation shield at 2 m above ground level.
in a radiation shield at 2 m above ground level.
Observations were recorded as an instantaneous value
Observations were recorded as an instantaneous value
every 30 minutes.
every 30 minutes.
The Surface temperature (Ts) is retrieved from the
The Surface temperature (Ts) is retrieved from the
Terra satellite and consists of the MODIS product
Terra satellite and consists of the MODIS product
MOD11A2 which provides an 8-day mean surface
MOD11A2 which provides an 8-day mean surface
temperature at 1km by 1km resolution. The mean
temperature at 1km by 1km resolution. The mean
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time of the satellite overpasses is 1030 local solar
time of the satellite overpasses is 1030 local solar
time (day) and 2230 local solar time (night).
time (day) and 2230 local solar time (night).
For comparison with Ts the mean air temperatures
For comparison with Ts the mean air temperatures
were taken at 1030 and 2230 EAT (East African
were taken at 1030 and 2230 EAT (East African
Time) averaged over the same 8 day periods as the
Time) averaged over the same 8 day periods as the
surface temperature were used
surface temperature were used.
.
4.2 Variables
4.2 Variables
Five variables were defined, four of which
Five variables were defined, four of which
represented day (1030) and night (2230) air and
represented day (1030) and night (2230) air and
surface temperatures. The novel variable Ts was
surface temperatures. The novel variable Ts was
defined as the difference between day and night
defined as the difference between day and night
surface temperatures (and is a proxy for solar
surface temperatures (and is a proxy for solar
radiation). Four variables were used as input and one
radiation). Four variables were used as input and one
variable was used as output (TaD)
variable was used as output (TaD).
.
Variables
Variables
Input/output
Input/output Variable
Variable Description
Description
output
output TaD
TaD Air temperature of day
Air temperature of day
inputs
inputs
TaN
TaN Air temperature of night
Air temperature of night
TsD
TsD Surface temperature of day
Surface temperature of day
TsN
TsN Surface temperature of night
Surface temperature of night
∆Ts
∆Ts Solar radiation
Solar radiation
=TsD - TsN
=TsD - TsN
T
TABLE
ABLE.1 V
.1 VARIABLES
ARIABLES
4.3 Models
4.3 Models
Using a benchmark model in machine learning is a
Using a benchmark model in machine learning is a
standard way of evaluating/comparing the
standard way of evaluating/comparing the
performance of novel models with an accepted
performance of novel models with an accepted
standard. The benchmark model is applied to our
standard. The benchmark model is applied to our
research data and results compared with the results
research data and results compared with the results
from the novel models. The benchmark model
from the novel models. The benchmark model
simulation was based on research presented in [27], in
simulation was based on research presented in [27], in
which ANFIS was used to predict air temperature.
which ANFIS was used to predict air temperature.
The air temperature was used as input and output. The
The air temperature was used as input and output. The
benchmark simulation used TaN as input and TaD as
benchmark simulation used TaN as input and TaD as
output.
output.
Four different sets of inputs as four novel models
Four different sets of inputs as four novel models
were evaluated for the first time to estimate daytime
were evaluated for the first time to estimate daytime
Ta. Different combinations of these variables each
Ta. Different combinations of these variables each
have a meaning in the context of climate change
have a meaning in the context of climate change
studies (see table 2).
studies (see table 2).
Models
Models
Model
Model Acronym
Acronym Inputs
Inputs Output
Output
Model-1
Model-1 m1
m1 TsN, TaN, TsD
TsN, TaN, TsD TaD
TaD
Model-2
Model-2 m2
m2 TsN, TsD
TsN, TsD TaD
TaD
Model-3
Model-3 m3
m3 TaN,
TaN, ∆Ts
∆Ts TaD
TaD
Model-4
Model-4 m4
m4 ∆Ts
∆Ts TaD
TaD
Table.2
Table.2 Models
Models
4.4 K-fold Cross Validation
4.4 K-fold Cross Validation
The selection of 4-fold cross validation as a
The selection of 4-fold cross validation as a
performance metric was based on the minimum of
performance metric was based on the minimum of
data rows available for one-fold.
data rows available for one-fold.
4.5 Data Sets
4.5 Data Sets
The following naming conventions and descriptions
The following naming conventions and descriptions
were used:
were used:
The testing data set contained 20% of the
The testing data set contained 20% of the
main data set and its objective was to test the
main data set and its objective was to test the
generalizability of the trained and cross
generalizability of the trained and cross
validated model with unseen data.
validated model with unseen data.
The learning data set contained 80% of the
The learning data set contained 80% of the
main data set from which the training (75%)
main data set from which the training (75%)
and checking (25%) data sets were selected
and checking (25%) data sets were selected
for 4-fold cross validation to prevent
for 4-fold cross validation to prevent
overfitting of the model. The average RMSE
overfitting of the model. The average RMSE
was calculated and used as the main
was calculated and used as the main
performance metric for each model.
performance metric for each model.
4.6 Data Preprocessing
4.6 Data Preprocessing
Requirements that determined data per-processing
Requirements that determined data per-processing
include:
include:
Two software were used. MATLAB ANFIS
Two software were used. MATLAB ANFIS
GUI [28] needed a special data preparation
GUI [28] needed a special data preparation
process. KNIME analytical platform [29]
process. KNIME analytical platform [29]
used the same data files prepared for
used the same data files prepared for
MATLAB.
MATLAB.
Machine learning analysis stages of training,
Machine learning analysis stages of training,
checking, and testing needed different data
checking, and testing needed different data
sets prepared for each stage.
sets prepared for each stage.
K-fold cross validation: 4-fold cross
K-fold cross validation: 4-fold cross
validation selected regarding the minimum
validation selected regarding the minimum
number of data rows needed for each fold.
number of data rows needed for each fold.
Data needed to be prepared for each fold
Data needed to be prepared for each fold
individually.
individually.
Variables needed to be extracted from the
Variables needed to be extracted from the
main data files.
main data files.
Novel models with different inputs needed
Novel models with different inputs needed
separate data sets.
separate data sets.
5
5Simulation Results
Simulation Results
5.1 Models RMSE
5.1 Models RMSE
Table 3 contains the RMSE (between observed
Table 3 contains the RMSE (between observed
and predicted Ta) for the four novel models (m1-
and predicted Ta) for the four novel models (m1-
m4) and the benchmark model (bm) using each
m4) and the benchmark model (bm) using each
of the five algorithms. Figures are the average
of the five algorithms. Figures are the average
RMSE of the 4-fold cross validation. The RMSE
RMSE of the 4-fold cross validation. The RMSE
unit is Celsius degrees and should be interpreted
unit is Celsius degrees and should be interpreted
in the context of the climate change studies in
in the context of the climate change studies in
which ‘’ errors generally fall in the 2–3 °C range
which ‘’ errors generally fall in the 2–3 °C range
while the level of precision generally considered
while the level of precision generally considered
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as accurate is 1–2 °C [30]. These accuracy ranges
as accurate is 1–2 °C [30]. These accuracy ranges
were regarded in interpreting the results.
were regarded in interpreting the results.
Model 4 is universally the poorest in
Model 4 is universally the poorest in
performance (RMSE between 3.5 and 4.7 C)˚
performance (RMSE between 3.5 and 4.7 C)˚
meaning that Ts (solar radiation) as a sole input
meaning that Ts (solar radiation) as a sole input
can not be used to estimate the air temperature in
can not be used to estimate the air temperature in
the forest zone. The other three models tend to be
the forest zone. The other three models tend to be
fairly similar and RMSE is usually between 2 and
fairly similar and RMSE is usually between 2 and
3 C (greyed). (see appendices, table 3)˚
3 C (greyed). (see appendices, table 3)˚
5.2 The Best Model
5.2 The Best Model
The best model in Table 3 is model-2 combined
The best model in Table 3 is model-2 combined
with the ANFIS algorithm. This model gained the
with the ANFIS algorithm. This model gained the
average (4-folds) RMSE = 2.0314 which is in the
average (4-folds) RMSE = 2.0314 which is in the
acceptable accuracy range while fold-3
acceptable accuracy range while fold-3
(fm2fold3) of this model gave and RMSE =
(fm2fold3) of this model gave and RMSE =
1.9899 as the best model in the testing stage with
1.9899 as the best model in the testing stage with
unseen data which is in the ideal accuracy range
unseen data which is in the ideal accuracy range
(1 2 C) Testing data in figure 3 is presented
(1 2 C) Testing data in figure 3 is presented
with blue dots where the FIS (Fuzzy Inference
with blue dots where the FIS (Fuzzy Inference
System) output is presented with red asterisks.
System) output is presented with red asterisks.
(see appendix, figure 3)
(see appendix, figure 3)
The correlation between model-2 inputs (TsN,
The correlation between model-2 inputs (TsN,
TsD) and the output (TaD) in the best model is
TsD) and the output (TaD) in the best model is
presented in figure 4. The smooth surface
presented in figure 4. The smooth surface
suggests a strong correlation between inputs and
suggests a strong correlation between inputs and
the output (see appendix, figure 4)
the output (see appendix, figure 4)
5.3 Model Ranking
5.3 Model Ranking
To compare the various model and algorithm
To compare the various model and algorithm
combinations in more detail they were ranked from
combinations in more detail they were ranked from
best performing (R1) to worst (R25) in Table 4. The
best performing (R1) to worst (R25) in Table 4. The
following points can be concluded:
following points can be concluded:
Model-1 was the best performing model for
Model-1 was the best performing model for
three algorithms, although it does contain the
three algorithms, although it does contain the
most inputs.
most inputs.
The best overall combination was model-2
The best overall combination was model-2
combined with ANFIS.
combined with ANFIS.
The best algorithm averaged across all
The best algorithm averaged across all
models was ANFIS.
models was ANFIS.
LIBSVM and Simple regression trees tended
LIBSVM and Simple regression trees tended
to perform relatively poorly overall (see
to perform relatively poorly overall (see
appendix, table 4)
appendix, table 4)
5.4 Model Reliability and Consistency Rankin
5.4 Model Reliability and Consistency Ranking
g
Table 5 summarizes the reliability and
Table 5 summarizes the reliability and
consistency rankings for each model. To
consistency rankings for each model. To
determine model reliability the mean ranking was
determine model reliability the mean ranking was
used. To determine model consistency the range
used. To determine model consistency the range
in the ranking (difference between best and worst
in the ranking (difference between best and worst
ranks) was used. A lower mean ranking presents
ranks) was used. A lower mean ranking presents
higher reliability. A lower variation in rankings
higher reliability. A lower variation in rankings
means higher consistency.
means higher consistency.
Models-1 is the best in reliability ranking
Models-1 is the best in reliability ranking
across all algorithms followed by models
across all algorithms followed by models
2 and 3. the differences in consistency
2 and 3. the differences in consistency
ranking reflect the differences between
ranking reflect the differences between
different input variables.
different input variables.
Model-4 did not work well in the forest
Model-4 did not work well in the forest
zone, therefore its high consistency
zone, therefore its high consistency
should be seen in the context of RMSE
should be seen in the context of RMSE
results gained by each algorithm (i.e. it is
results gained by each algorithm (i.e. it is
consistently poor)
consistently poor)
Model-2 and Model-1 have the same
Model-2 and Model-1 have the same
ranking variation of 17, but Model-2 has
ranking variation of 17, but Model-2 has
lower boundaries than Model-1 so has
lower boundaries than Model-1 so has
been ranked as third best in consistency
been ranked as third best in consistency
ranking.
ranking.
The benchmark model comes after novel
The benchmark model comes after novel
models m1, m2, and m3 in reliability
models m1, m2, and m3 in reliability
ranking whereas in the consistency
ranking whereas in the consistency
ranking is the last.
ranking is the last.
Models Reliability and Consistency Ranking
Models Reliability and Consistency Ranking
Model
Model Ranking
Ranking
Average
Average
Reliability
Reliability
Ranking
Ranking
Ranking
Ranking
Variation
Variation
Consistency
Consistency
Ranking
Ranking
m1
m1 9.2
9.2 1
117
17 4
4
m2
m2 9.8
9.8 2
217
17 3
3
m3
m3 10
10 3
313
13 2
2
m4
m4 22.2
22.2 5
55
51
1
bm
bm
13.8
13.8 4
420
20 5
5
Table.5 Models reliability and consistency
Table.5 Models reliability and consistency
ranking
ranking
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5.5 Algorithm Reliability and Consistency
5.5 Algorithm Reliability and Consistency
ranking
ranking
The same concepts were used to determine the
The same concepts were used to determine the
reliability and consistency rankings of each
reliability and consistency rankings of each
algorithm in table 6. ANFIS came up as the best
algorithm in table 6. ANFIS came up as the best
algorithm in reliability ranking across all models
algorithm in reliability ranking across all models
followed by Polynomial regression and Linear
followed by Polynomial regression and Linear
regression algorithms. Linear regression is the
regression algorithms. Linear regression is the
most consistent. The differences in consistency
most consistent. The differences in consistency
ranking should be referred as differences between
ranking should be referred as differences between
algorithms and models. The most reliable
algorithms and models. The most reliable
algorithms are not the most consistent in
algorithms are not the most consistent in
performance.
performance.
Algorithms Reliability and Consistency Ranking
Algorithms Reliability and Consistency Ranking
Algorithm
Algorithm Ranking
Ranking
Average
Average
Reliability
Reliability
Ranking
Ranking
Ranking
Ranking
Variation
Variation
Consistency
Consistency
Ranking
Ranking
ANFIS
ANFIS 6
61
119
19 5
5
Polynomial
Polynomial
regression
regression
9.8
9.8 2
217
17 4
4
Linear
Linear
regression
regression
15
15 3
39
91
1
SVM
SVM 15.2
15.2 4
416
16 3
3
Simple
Simple
regression
regression
tree
tree
19
19 5
59
92
2
Table.6, Algorithms Reliability and Consistency
Table.6, Algorithms Reliability and Consistency
Ranking
Ranking
5.6 Performance Evaluation
5.6 Performance Evaluation
The performance of novel models was compared
The performance of novel models was compared
with the benchmark model. Overall the novel
with the benchmark model. Overall the novel
models outperformed the benchmark model:
models outperformed the benchmark model:
100% (four out of four models) better in
100% (four out of four models) better in
the consistency comparison
the consistency comparison
75% (three out of four models) better in
75% (three out of four models) better in
the reliability comparison
the reliability comparison
6
6Discussion
Discussion
The forest zone of Kilimanjaro has a generally stable
The forest zone of Kilimanjaro has a generally stable
temperature regime with slow changes that make it
temperature regime with slow changes that make it
relatively easy to predict Ta from Ts, in comparison
relatively easy to predict Ta from Ts, in comparison
with other environments on the mountain (not shown
with other environments on the mountain (not shown
in this paper) which can experience rapid fluctuations.
in this paper) which can experience rapid fluctuations.
Therefore both Ts and Ta show considerable memory
Therefore both Ts and Ta show considerable memory
from day to day and can be used for predicting each
from day to day and can be used for predicting each
other. Models 1 and 2 both work well and both
other. Models 1 and 2 both work well and both
include Ts during the day and night. This implies high
include Ts during the day and night. This implies high
coupling between air and simultaneous surface
coupling between air and simultaneous surface
temperatures. A proxy for solar heating alone (model
temperatures. A proxy for solar heating alone (model
4) is less successful, both due to the high number of
4) is less successful, both due to the high number of
cloudy days, and the fact that temperature is
cloudy days, and the fact that temperature is
controlled as much by transpiration and latent heat
controlled as much by transpiration and latent heat
flux in the forest, as it is by direct energy balance.
flux in the forest, as it is by direct energy balance.
In the forest, the “surface” temperature is actually
In the forest, the “surface” temperature is actually
strongly influenced by the canopy of the forest (up to
strongly influenced by the canopy of the forest (up to
20-30m above ground level) which is measured as the
20-30m above ground level) which is measured as the
effective surface by the satellites. This canopy
effective surface by the satellites. This canopy
temperature is quite well coupled with air temperature
temperature is quite well coupled with air temperature
within the forest, thus explaining the success of the
within the forest, thus explaining the success of the
models which use Ts as a predictor for Ta.
models which use Ts as a predictor for Ta.
Higher up the mountain where there is much less
Higher up the mountain where there is much less
vegetation, the surface measured by the satellite is
vegetation, the surface measured by the satellite is
much nearer ground level, and it is likely to be
much nearer ground level, and it is likely to be
decoupled from the air temperature measured at 2 m
decoupled from the air temperature measured at 2 m
well above the vegetation. Therefore additional work
well above the vegetation. Therefore additional work
will be required to transfer these findings to other
will be required to transfer these findings to other
environments on the mountain and elsewhere.
environments on the mountain and elsewhere.
This research used the zone data to cover the forest
This research used the zone data to cover the forest
area. There are four stations in this area. Three
area. There are four stations in this area. Three
stations are located on the north-east wall and the
stations are located on the north-east wall and the
fourth is located on the south-west wall of
fourth is located on the south-west wall of
Kilimanjaro reviving different levels of solar
Kilimanjaro reviving different levels of solar
radiation. Further research can focus on the stations
radiation. Further research can focus on the stations
to investigate the impact of the location on the
to investigate the impact of the location on the
models.
models.
7
7Conclusion
Conclusion
The research confirms the reliability of machine
The research confirms the reliability of machine
learning algorithms (especially ANFIS) to estimate
learning algorithms (especially ANFIS) to estimate
air temperature from satellite-measured surface
air temperature from satellite-measured surface
temperature in a remote forested environment with
temperature in a remote forested environment with
few measured climate variables. The coupling
few measured climate variables. The coupling
between air temperature and surface temperature
between air temperature and surface temperature
ensures model success in the forested zone of
ensures model success in the forested zone of
Kilimanjaro. The results could be applicable to other
Kilimanjaro. The results could be applicable to other
forested areas. Further research however is required to
forested areas. Further research however is required to
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apply this approach to other areas and land-cover
apply this approach to other areas and land-cover
types on the mountain, and further afield.
types on the mountain, and further afield.
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Appendix
:
Models RMSE
Models Inputs ANFIS Polynomial
regression
Linear
regression
LIBSVM Simple
regression tree
Average
RMSE
m1 TsN, TaN, TsD
TsN, TaN, TsD 2.042025 2.12 2.337 2.204 2.973 2.335205
m2 TsN, TsD
TsN, TsD 2.0314 2.182 2.441 2.262 2.934 2.37008
m3 TaN, Ts
TaN, Ts2.069875 2.2 2.442 2.23 2.827 2.353775
m4 TsTs3.667775 3.689 3.686 4.186 4.758 3.997355
bm TaN
TaN 2.08345 2.214 2.478 4.186 2.88 2.76829
Average RMSE 2.378905 2.481 2.6768 3.0136 3.2744
T
TABLE
ABLE.3 M
.3 MODELS
ODELS RMSE
RMSE
Figure 4: The Best Model Surface Plot
Figure 4: The Best Model Surface Plot
Models Ranking
Models Ranking
Models
Models Inputs
Inputs ANFIS
ANFIS Polynomial
Polynomial
regression
regression
Linear
Linear
regression
regression
LIBSVM
LIBSVM Simple regression
Simple regression
tree
tree
m1
m1 TsN, TaN, TsD
TsN, TaN, TsD R2
R2 R5
R5 R12
R12 R8
R8 R19
R19
m2
m2 TsN, TsD
TsN, TsD R1
R1 R6
R6 R13
R13 R11
R11 R18
R18
m3
m3 TaN, Ts
TaN, TsR3
R3 R7
R7 R14
R14 R10
R10 R16
R16
m4
m4 TsTsR20
R20 R22
R22 R21
R21 R23
R23 R25
R25
bm
bm TaN
TaN R4
R4 R9
R9 R15
R15 R24
R24 R17
R17
T
TABLE
ABLE.4 M
.4 MODELS
ODELS R
RANKING
ANKING
Figure 3: The Best Model Test Results
Figure 3: The Best Model Test Results
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