A Study of Human Physiological Comfort in Lagos Metropolis Using Landsat Satellite Imagery Between 1984 and 2013

Our cities today are exposed more too urban atmospheric conditions that influence man’s comfort, health and behavior. As cities grow changes in land use have altered man’s physiological comfort experienced today. Landsat satellite imagery was used to study human physiological comfort in Lagos metropolis between 1984 and 2013. So, to achieve this remote sensing data acquired from Landsat satellite imagery and Geographic Information System (GIS) were used to derive, namely: land use land cover, land surface and air temperature, and relative humidity index for 1984, 2000 and 2013. While Temperature Humidity Index (THI) was computed from air temperature and relative humidity index which was used to assess human physiological out-door comfort in relation to land use activities. In this study, the health implications of physiological stress and thermal sensation were highlighted and addressed from the environmental and health perspectives as it relates to land use. This study thrown open the door of environmental efficiency, well-being and the health of citizens which is influenced by physiological comfort through developing and maintaining comfortable environmental conditions that will enhance the quality of urban life.


Introduction
Cities land surfaces are made from different urban materials and morphology which have significant thermal properties and reflectance with different heat capacity, thermal conductivity and surface radiative properties (albedo and emissivity)

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Engineering (JIEEE) A2Z Journals when compared with surrounding rural areas [1].This alteration therefore inevitably results in the redistribution of incoming solar radiation, thereby inducing urban-rural contrasts, in surface radiance and air temperatures [1], [2].Thus, changes in energy fluxes in urban areas often led to higher temperatures, which alter human thermal comfort observed in cities. Human health and thermal comfort are affected more by climate than by any other element of man's physical environment [3].The effects of climate on man, particularly his thermal comfort, physical and mental efficiency, constitute a major theme of the science of human biometeorology.Thermal comfort therefore can be defined as a state of feeling in which a person has no wish to increase or decrease insulation or to adjust the ambient thermal environment [4].Temperature is the most significant component in the experience of comfort in a space [5].
Various aspects of humanity are concerned with the visual, acoustic and thermal components of the surrounding environment [6].Human beings are sensitive to slight temperature changes yet cannot perceive differences in relative humidity levels within the range of 60% and above.However, people vary, sometimes markedly, in their feeling of comfort according to their metabolic rate, type of clothing, workload, age, diet, emotions, cultural influences, past climatic experience and climatic zone among others.Thus, women generally prefer slightly higher air temperatures than men.People from the tropical regions tend to accept as comfortable higher levels of air temperature and humidity than people from temperate zones.
Outdoor workers also tolerate higher temperatures than sedentary workers while older individuals tend to prefer warmer conditions than younger individuals [7], [8].
Our cities today are exposed more too urban atmospheric conditions that influence man's comfort, health and behavior.
Weather conditions play a vital role in the growth and propagation of disease, but per se does not cause disease but determine the type and population of diseases pathogens prevalent in a given area.The heat exchange between the human body and his environment is governed by radiation, convection, and evaporation.It is the heat imbalance that the body reacts to and restores through various physiological responses [9].But physiological responses of man to work, play, reaction and to other environmental condition depend on the interaction between man, his environment and weather [10].According to Ayode [9], physiologic comfort is determined by both meteorological and non-meteorological factors.The thermal factors comprise such meteorological variables as air temperature, air humidity, wind velocity, short and long wave radiation, which have a thermo-physiological effect on man's outdoors and indoors activities; the significance to health and tourism is associated with thermoregulation and circulatory regulation [11],[12].
This study aims at understanding human physiological comfort in Lagos metropolis using Landsat satellite imagery as a measure to analyze comfort, health and the environment as key issues in our urban -climate system.Most research carried out was done outside Lagos with few works dealing with the urban climate in Lagos metropolis.However, one striking feature observed in reviewing few studies in Thermal Humidity Index (THI) in Lagos metropolis is the lack of the urban climate as well as remote sensing as input parameters in their consideration.So, this research adopts the use of remote sensing data and Geographic Information Systems (GIS) technique as tools to study human physiological comfort in Lagos metropolis.In order to address this knowledge gap, we estimate land surface and air temperature, and relative humidity index between 1984 and 2013 (a span of 29 years) across Lagos metropolis to improve our understanding of the thermal environment.While THI for Lagos metropolis in 1984, 2000 and 2013 was computed and used to classify human physiological comfort zones.The purpose of this study is to investigate the thermo-physiological comfort using Physiological Equivalent Temperature (PET) which was used to characterize the outdoor environment and their impact on human thermal comfort based on the different climatic characteristics experienced in Lagos metropolis.This approach is a quantitative approach which gives us a detailed view of thermal discomfort zone in Lagos metropolis.For proper comprehension, the study is divided into the following: 1.
Effect of changes in land use on Lagos metropolis; 2. Effect of changes in temperature on Lagos metropolis; 3. Effect of changes in relative humidity index on Lagos metropolis; 4. Effect of changes in temperature humidity index (THI) on Lagos metropolis; and 5. Effect of changes in thermal human comfort on Lagos metropolis using GIS techniques.

Methodology
Where, offset, gain, K1 and K2 = User defined parameters, Lλ = Cell value as radiance (W/m -2 sr -1 μm -1 ), DN= Digital number of the thermal imagery, Lmax and Lmin = Derived temperature depending on gain status, ML = Band-specific multiplicative rescaling factor, AL = Band-specific additive rescaling factor, Qcal = Quantized and calibrated standard product pixel values (DN), and TB = Blackbody temperature.Land Surface Temperature (LST) (K) (in degree Kelvin) was derived based on the blackbody temperature using equation 4. The conversion was carried out through the following: Where, TLST (K) = Land Surface Temperature (in degree Kelvin); λ= Wave length of emitted radiance (11.5μm 6.626×10 -34 Js, and ε = Emissivity in the range between 0 and 1. Emissivity (ε) was computed using NDVI (Normalized Difference Vegetation Index) [15] expressed as: Where, H = Sensible heat flux (W/m -2 ), ρair = Density of air humidity (kgm -3 ), CP= Air specific heat in constant pressure (J/Kg -1 K -1 ), Ts = LST (K), Ta= Air temperature (K), and raH = Aerodynamic resistance (sm -1 ).The result was converted from degree Kelvin to degree Celsius using equation 8.The derived output was used as input in computing Temperature Humidity Index (THI) and used in studying the effect of changes in temperature on Lagos metropolis.Air temperature values derived from Landsat imagery were validated using in-situ data from NIMET meteorological station with respect to its mean, using Spearman's rho non-parametric correlation model in SPSS 20 software.
Temperature Humidity Index (THI) was used to investigate human comfort in Lagos metropolis for 1984, 2000 and 2013.This method produces an index for studying the effects of heat condition on human comfort and could be derived from air temperature and relative humidity using equation 10 [18] below: In order to study human comfort, Physiological Equivalent Temperature (PET) a thermo-physiological index was used to model thermal conditions of the human body in a physiologically relevant way.This was derived from THI in equation 10 for 1984, 2000 and 2013.In this study, an elaborate attempt was made to classify THI output into different grades of thermal sensations and physiological stress using the criteria listed in Table 2 for Lagos metropolis.The derived output was used to study the effect of changes in human comfort on Lagos metropolis using the LULC and the administrative area for 1984, 2000 and 2013.

Results and Discussion
For proper comprehension, the study is divided into the following: 1.Effect of changes in land use on Lagos metropolis, 2.
effect of changes in temperature on Lagos metropolis, 3. effect of changes in relative humidity index on Lagos metropolis, 4.
effect of changes in temperature humidity index on Lagos metropolis, and 5. effect of changes in thermal human comfort on Lagos metropolis between 1984 and 2013.

1. Effect of changes in Land use on Lagos metropolis
Based on the adopted land use/land cover (LULC) classification, Figure 2 shows the LULC of Lagos metropolis for 1984, 2000 and 2013 while  3 reveals that built-up areas increase at the expense of agricultural land, water bodies, wetland, and forest land.In s p i t e of these changes in LULC, prompt variations in temperature were observed to accompany these changes in Lagos metropolis.
Furthermore, the rapid depletion of vegetation cover has reduced the natural cooling effects of shades a n d evapotranspiration of p l a n t s and shrubs which has increased the urban discomfort experienced in Lagos metropolis.

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Engineering (JIEEE) A2Z Journals     4a shows changes in the Land Surface Temperature (LST) of land use/land cover while Table 4b shows changes in the air temperature of land use/land cover in Lagos metropolis between 1984 and 2013.From the result presented in Table 4 based on LULC, LST as well as air temperature is high for public/educational institution and commercial/industrial service, and then followed by high density residential area and bare ground/open space.4), this in-turn has increased the difference between surface and air temperature which also, has made surface temperature higher.Validation was performed using meteorological data from weather station compared with derived air temperature from thermal infrared band (using Landsat satellite imagery) for 1984, 2000 and 2013, and the results reveals that the relationship is statistically significant (Fcal>Ftab=12.62 > 0.18) at 95% level of confidence with R 2 = 85.70%.

Effect of changes in Relative Humidity Index on Lagos metropolis
Relative humidity index (RHI) for Lagos metropolis was estimated from Landsat-TM 5, ETM+ 7 and O L I 8 thermal imagery as represented in Figure 5.

Conclusion
This research described the methodology and findings obtained from an outdoor thermal comfort study carried out in Lagos metropolis.This study design has proved to be appropriate to acquire land surface and air (atmospheric) temperature, and relative humidity index values for 1984, 2000 and 2013 using Landsat satellite imagery which was used to model thermal humidity index appropriate to study human physiological stress and thermal sensation.Also, thermal humidity index has thrown some light on the possible behavioral reactions of people to the overall thermal conditions and how land use activities have influenced it.This research has highlighted the importance of physiological stress on workers performances, tourism, home comfort, education, and sites selection which are of importance to government, planners, educationist, and other stakeholders that hold the environment so dear to them.The high rate of heat stress on the environment was found to have an effect on the health of the people which could lead to heat related diseases such as fatigue, sunstroke, muscle cramps, heat stroke and heat exhaustion.This study has thrown open the door of environmental efficiency, well-being and the health of the citizens which is positively (or negatively) influenced by thermal comfort and physiological stress, by developing and maintaining comfortable environmental conditions that will enhance the quality of urban life.
6) Where, ε = Composite emissivity, εv = Vegetation emissivity, εs = Soil emissivity, and ʄv = Fractional vegetation cover.Fractional vegetation cover was computed using equation 7 [16] expressed as: Journal of Informatics Electrical and Electronics Engineering (NDVIMax = NDVI for a complete vegetation cover and NDVIMin = NDVI for bare soil.NDVIMax and NDVIMin were assigned NDVI values derived from Landsat TM 5 for 1984, ETM+ 7 for 2000 and OLI 8 for 2013.The coefficient α is a function of leaf orientation distribution within the canopy, where erectophile to planophile canopies have values between 0.6 and 1.25.A value of 0.6 was used in the current investigation.The fractional vegetation cover was compared with limited ground observations and the results were consistent.Emissivity was then estimated using the derived fractional vegetation cover and the specified emissivity values of soil and vegetation in equation 7. Using equation 8, the Land Surface Temperature (LST) was converted from degree Kelvin to degree Celsius: (°C) = Land Surface Temperature in degree Celsius (°C) and TLST (K) = Land Surface Temperature in degree Kelvin (K).The derived output was used as input in computing air temperature and also used in studying the effect of changes in temperature on Lagos metropolis.Air temperature was estimated from sensible heat flux [17] using equation 9 below ex- = Temperature Humidity Index (°C); Ta= Air temperature; 0.81 and 500 = Constant factors for wet and dry climate regions[19], while RHI = Relative humidity index (%) and this was derived using equation 11 below expressed as: , RHI = Relative Humidity Index (%), ea = Actual water vapor pressure (Kpa), and es = Saturate water vapor pressureJournal of Informatics Electrical and ElectronicsEngineering (JIEEE) A2Z Journals (Kpa).The derived output (THI) was used to study the effect of changes in THI on Lagos metropolis using the LULC and administrative area for 1984, 2000 and 2013.
It is observed that variations in temperature are mainly due to the kind of activities that go on in the various land use.Reduction in forest/natural landscape has increased and modified the micro-climate of Lagos metropolis due to the replacement of depleted vegetation cover/open land with impervious surfaces which has robbed the city of the natural cooling effects provided by shade and evapotranspiration of plants and shrubs.Surface and air temperature has increased in high and low density residential area, commercial/industrial service, and public/educational institution compared to U. Ibeabuchi et al.ISSN (Online) : 2582-7006 10 Journal of Informatics Electrical and Electronics Engineering (JIEEE) A2Z Journals forest and natural landscape (Table

3. 4 .
Effect of changes in Temperature Humidity Index (THI) on Lagos metropolis Temperature Humidity Index (THI) in Lagos metropolis was estimated from air temperature and relative humidity index derived from Landsat-TM 5, ETM+ 7 and O L I 8 thermal imagery for 1984, 2000 and 2013 as presented by Figure 6.Table 6 shows changes in the distribution of THI for the LULC of Lagos metropolis between 1984 and 2013.In Lagos metropolis, the minimum THI of 15.38°C for 1984, 17.21°C for 2000, and 20.91°C for 2013 was observed.While maximum THI of 25.88°C for 1984, 31.51°C for 2000 and 32.91°C for 2013 was observed.THI means 22.13°C for 1984, 24.86°C for 2000 and 28.18°C for 2013 was observed.
Oshodi met (meteorological) station, Lagos Nigeria.The study area covers Lagos metropolis which is located within Lagos state as shown in Figure 1, created in 1967 [13].Lagos metropolis lies in Southwestern Nigeria, on the Atlantic coast.It is located between longitude 3° 4' East to 3° 40' East and between latitudes 6° 23' North to 6° 42' North [14].Lagos metropo- lis covers 1171km 2 area of which 221km 2 is Lagoons and waterways.

Table 1 .
Landsat TM, ETM+ and OLI sensor and characteristics.
* TIRS -Thermal Infrared SensorThe temperature of Lagos metropolis was extracted using Landsat satellite imagery; two parameters were derived, namely: land surface temperature and air temperature.Land Surface Temperature (LST) was derived from thermal band (from TIRS in Table1) of Landsat TM 5 for 1984 in equation 1(insert band 6), ETM+ 7 for 2000 in equation 2 (insert band 6.2) and OLI 8 for 2013 in equation 3 (insert band 10) as stated below using Idrisi Selva software:

Table 2 .
Physiological Equivalent Temperature (PET) (°C) class for thermal sensation and physiological stress in Nigeria.
Table 3 shows the LULC changes between 1984 and 2013.Agricultural area decreased from 155.74Km 2 in 1984 to 116.89Km 2 in 2000, and then to 16.96Km 2 in 2013.While commercial/industrial area and public/educational institution increased from 23.52Km 2 to 104.58Km 2 and 62.03 Km 2 to 133.23 Km 2 from 1984 to 2000 and decreased to 45.57Km 2 and 73.10 Km 2 in 2013.Forest land decreased from 109.52Km 2 to 39.95Km 2 from 1984 to 2000, and then to 30.25Km 2 in 2013.Low density residential area increased from 168.11Km 2 to 171.76Km 2 and then to 240.78Km 2 while high density residential area increased from 65.35Km 2 to 68.20Km 2 and then to 159.59Km2 for 1984, 2000 and 2013.Result in Table

Table 3 .
Changes in Land Use/Land Cover (LULC) of Lagos metropolis between 1984 and 2013.Land Use/

Table 4 .
(a) Changes in Land Surface Temperature (LST) of the Land Use/Land Cover (LULC) for Lagos metropolis between 1984 and 2013; and (b) changes in air temperature of the Land Use/Land Cover (LULC) between 1984 and 2013 for Lagos metropolis.
The minimum, maximum, and mean relative humidity index for 1984, 2000 and 2013 is presented in Table5.In Lagos metropolis, 82.16% minimum and 88.28% maximum with a mean relative humidity index of 85.79% was observed for 1984.A relative humidity index of 87.55% minimum and 94.01%maximum with a mean of 90.94% was observed for 2000.While in 2013, 97.58% minimum and 98.63% maximum with a mean relative humidity index of 98.12% for 2013 was observed.Based on the result, relative humidity index was found to be high throughout the year and may not be less than 82.00% to 99.00% in Lagos metropolis as confirmed byAbegunde [14].

Table 6 .
Changes in Thermal Humidity Index (THI) (°C) of the Land Use/Land Cover (LULC) for Lagos metropolis between 1984 and 2013.