Assessment of Aboveground Biomass-Vegetation Storage in Urban

Centres Using Remote Sensing Technology

Víctor Hugo González Jaramillo

and María Zapata

Departamento de Ingeniería Civil, Universidad Técnica Particular de Loja, Marcelino Champagnat, Loja, Ecuador

Escuela de Ingeniería Civil, Universidad Técnica Particular de Loja, Marcelino Champagnat, Loja, Ecuador

Keywords: Vegetation, Biomass, Remote Sensing, Unmanned Aerial Vehicle (UAV).

Abstract: Urban centres have grown rapidly, expanding into areas that were previously used for agriculture or were

occupied by natural vegetation such as forests. The development of human and productive activities has

increased environmental degradation and pollution through greenhouse gas emissions, which further

aggravates the aforementioned problems and increases the effects of climate change. One of the main

pollutants is CO

, which contributes to the warming of the earth's surface, but it can be removed from the

atmosphere by vegetation and stored as biomass. In urban centres, the lack of vegetation cover directly affects

the processes of air purification and carbon storage. This is why quantifying and monitoring the vegetation

cover is crucial in urban environments. This monitoring can be done through remote sensing techniques

supported by traditional processes such as data collection in the field. For this study, it was used satellite data

from Sentinel 2 and data from an unmanned aerial vehicle (UAV). The obtained results indicate a scarce of

vegetation cover within the urban centre.

1 INTRODUCTION

Nowadays, due to the increase in population and its

productive and industrial activities, cities are the main

sources of pollution and emission of greenhouse

gases (Chen, 2015; Liang et al., 2017), which go

directly to the atmosphere, affecting the environment.

These gases threaten the health of living beings that

inhabit a certain sector, but their effects expand

globally (Manisalidis et al., 2020). According to data

provided by the World Health Organization

(Sivaramanan, 2014), there are around 3.7 million

premature deaths due to air pollution, numbers that

are continually increasing due to excess emissions

from productive activities, industries and automobile

circulation (Roser, 2021). Cities are among the main

sources of emission of polluting gases such as CO

which is one of the main pollutants and generator of

global warming (Sood & Vyas, 2017). That is why

cities are also pioneers in finding ways to mitigate the

damage and collateral effects caused by pollution

(Chen, 2015).

https://orcid.org/0000-0002-2150-7690

To address the problem of the negative effects of

polluting and greenhouse gas emissions, the use and

implementation of urban green areas has been

proposed as an alternative (Badach et al., 2020;

Diener & Mudu, 2021), because vegetation purify the

water, the air, sequester C0

from the atmosphere and

release oxygen.

In continental Ecuador during the last decades

there has been a strong decrease in plant cover, where

different ecosystems have been affected, especially

primary forests (González-Jaramillo et al., 2016),

where not only is there complete deforestation, but

practices of selective extraction of commercial

species are carried out. Thus, near the populated

areas, the pressure of demographic growth and the

expansion of the urban area have generated the

decrease and degradation of vegetal covers. One of

these urban centres is the city of Loja, which in recent

years has shown accelerated population growth due to

the migration of people from rural to urban areas, thus

triggering the expansion of the urban area and

generating a considerable decrease in plant cover

(Tello, 2012). The city of Loja currently does not

have information on the vegetation cover within the

Jaramillo, V. and Zapata, M.

Assessment of Aboveground Biomass-Vegetation Storage in Urban Centres Using Remote Sensing Technology.

DOI: 10.5220/0011893500003536

In Proceedings of the 3rd International Symposium on Water, Ecology and Environment (ISWEE 2022), pages 46-51

ISBN: 978-989-758-639-2; ISSN: 2975-9439

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

city and previous reports such as INEC (2012), place

the cantonal head well below the reference minimum

threshold. For this reason, the objective of this

research is to use data from remote sensors to

determine the amount of existing vegetation cover in

the urban area, specifically in the vegetation of the

banks of the rivers and main parks of the city, this to

estimate the accumulated biomass and therefore its

carbon storage capacity.

2 STUDY AREA, MATERIALS

AND METHODS

2.1 Study Area

The city of Loja is located in the south of the Republic

of Ecuador at 2,100 m above sea level and has a land

area of 5,757.14 ha. In addition, the city is crossed

from south to north by two low-flow rivers

(Malacatos and Zamora), both intersect downstream

of the city to form the Jipiro River. In the urban centre

there are 21 types of vegetation cover (Villa, 2009),

among which are dominant tree species such as:

arupo, cascarilla, molle and sauce llorón (Salix

babylonica L.) (Alcaldía de Loja, 2015).

2.2 Materials and Methods

2.2.1 Satellite Data and Its Processing

In the present research work, Sentinel 2B images have

been used at level 1C with 10m of spatial resolution,

corresponding to the dates of 11/18/2017 and

07/31/2019. The satellite images were processed in

QGIS 3.4.12, with the Semi-Automatic Classification

Plugin (SCP) tool. To do this, a dark object correction

is performed to reduce the haze effect in the image

(Congedo, 2021), then cloud masking is applied to

use only pixels free of contamination. With the valid

pixels of the satellite images, the Normalized

Difference Vegetation Index (NDVI) was calculated

(Bhandari et al., 2012), where the NIR and RED band

are used. Simultaneously, the delimitation of the

vegetation cover of Loja city was carried out, for

which the information available in Google Satellite

was used, and which was obtained through the QGIS

QuickMapServices complement.

Subsequently, the amount of AGB was estimated

using the equation proposed by (Das & Singh, 2016),

as can be seen in Equation (1), where the previously

estimated NDVI value intervenes. From the

calculated AGB it was possible to estimate the

amount of stored carbon (C).

324.2* 14.18

mean

AGB NDVI=+

)

Where:

AGB corresponds to Above Ground Biomass

NDVI

mean

corresponds to NDVI mean value

To estimate the amount of carbon stored (C), the

obtained AGB value is multiplied by a factor of 0.5,

which will give the mean AGB value.

2.2.2 Aerial Photographs Obtained with

UAV and Their Processing

Having a relatively large land area (5,757.14 ha), it is

not possible to cover the entire study area by UAV

flights. For this reason, 4 areas within the city were

selected for data collection (La Argelia, Parque

Lineal, Parque Recreacional Jipiro and Kartodromo).

In each zone, between 9 and 11 ground control points

(GCP) were placed, whose coordinates were obtained

with the help of a differential global positioning

system (GPS). Plots were also established within each

zone, in Argelia 5 plots were placed, in the Parque

Lineal 6 plots were placed, in the Jipiro zone 5 plots

and the Kartodromo zone 6 plots were placed.

Regarding the technical characteristics of the

overflights, a UAV Mapper platform with a 24.24

megapixel fixed focal camera, known as Ricoh GR

III, was used. The flight was executed considering a

double grid, with a horizontal and lateral overlap of

80%. The UAV flew over at a height of 110 m with a

speed of 18 m/s.

The obtained aerial photographs were processed

in the Pix4D software using photogrammetric

techniques, generating point clouds and orthomosaics

for each zone. From the 3D point clouds using the

FUSION 3.7 tool, digital terrain models (DTM) and

digital surface models (DSM) were generated. From

these data, an individual tree classification was

obtained (Iizuka et al., 2018; Wilkes et al., 2018), and

the variables of tree height (H) and diameter at breast

level (DBH) were derived (da Silva Scaranello et al.,

2012; González-Jaramillo et al., 2018). The derived

data are required for the estimation of aerial biomass

in the allometric equation proposed by Chave et al.

(2005), as can be seen in Equation 2. The amount of

carbon stored is considered to be half the value

obtained from AGB.

()

0.940

0.0776AGB D H

)

Assessment of Aboveground Biomass-Vegetation Storage in Urban Centres Using Remote Sensing Technology

Where:

AGB corresponds to Above Ground Biomass

D corresponds to chest height diameter

H corresponds to overall height

ρω corresponds to wood density

For the wood density, reference values have been

taken based on the species present in the research

area. The assumed value was 0.59 gr/cm3 based on

the species reported by Tello (2016).

2.2.3 Vegetation Measurements

The measurement of the vegetation was carried out

within the plots selected for the survey by means of

UAV. For this, a diametric tape and a hypsometer

model Vertex 5 of the HAGLOF brand were used. For

this purpose, there were measured only trees. The

position of each tree is obtained from high-resolution

satellite images. In the field, the variables to be

measured correspond to tree height (H) and diameter

at breast height (D).

3 RESULTS AND DISCUSSION

3.1 Total Estimation of Biomass and

Carbon through Satellite Images in

the City of Loja

Through the digitization of high-resolution satellite

data, a total of 86.38 ha of vegetation cover was

obtained in the city of Loja, where 59.01 ha

correspond to vegetation cover on riverbanks and

27.37 ha correspond to parks. The total area obtained

represents 1.48% of the total territorial extension of

the area occupied by the city. Figure 1 shows the

process, where the vegetation has been delimited.

This process was done using high resolution satellite

images using the QGIS QuickMapServices plugin.

Figure 2 shows the delimitation of the city of Loja,

where through the Senstinel 2B satellite images the

NDVI values have been calculated for the study dates

(years 2017 and 2019). The images used for the

comparison correspond to different months (July and

November), this due to the high level of cloud cover

in the area, for which it was not possible to have

images for the same month.

For the estimation of AGB and C through the use

of satellite images, only the total area of existing

vegetation cover on the riverbanks and city parks has

been taken into consideration, which was estimated

and mentioned in this section (Figure 1). In the

satellite image corresponding to 11/18/2017, a total

of 12,797.31 Tn of AGB and 6,398.66 Tn of C were

obtained. In the satellite image corresponding to

07/31/2019, a total of 13,474.46 Tn was obtained of

AGB and 6737.23 tons of C.

Figure 1: Figure 1: Delimitation of vegetation cover in the

city of Loja.

Figure 2: Normalized Difference Vegetation Index (NDVI);

a) November 11, 2017, b) July 31, 2019.

3.2 Total Estimation of Biomass and

Carbon using UAV in the City of

Loja

The processed data from the 4 selected areas made it

possible to obtain the initial data for the development

of the study. For this, the photographs were processed

with the Pix4D software. Figure 3 shows the

delimitation of one of the sites and the distribution of

the GCPs used in the processing.

ISWEE 2022 - International Symposium on Water, Ecology and Environment

From the photographs obtained by each site,

products such as the point cloud and orthophotos are

obtained (Figure 4), which will serve for subsequent

analysis. From the point cloud, it is possible to

determine the DTMs and DSMs that were the basis

for the individual tree detection and the subsequent

processing for the AGB estimation.

Figure 3: Delimitation of the zones in the urban area in the

city of Loja and installation of the GCPs. This area

corresponds to Jipiro.

Figure 4: Cloud of points in the Argelia area

Table 1 shows the values obtained for each zone

according to the detection of individual trees, from

which the height of each tree, DBH and AGB values

were estimated. In this case, the mean values are

presented.

Table 2 shows the area that represents each of the

study zones and the values obtained for each zone for

AGB and for C. The estimate for each of the zones

consists of adding all the trees present in the zone.

Conventionally, average values are given in Tn/ha,

but in this case the AGB content is presented for an

entire area. With subsequent calculations, the mean

values can be obtained and represented in a

conventional manner with a distribution per ha (Table

3).

Table 1: Values obtained at individual tree level and its

parameters.

N° of

trees

H (m)

DBH

(cm)

AGB

(Tn)

Zones Mean Mean

Mean

Argelia 524 27,23 106,90

18,95

Parque

Lineal

432 19,00 51,01

2,80

Jipiro 995 20,53 60,01

4,31

Kartodromo 1136 18,72 49,61

2,61

Table 2: Study zones with total coverage and estimation of

AGB and C expressed in Tn.

Zones Area

(ha)

AGB (Tn) C (Tn)

elia 20,35 630,08 316,30

Parque Lineal 7,49 145,45 73,83

iro 16,72 433,67 219,19

Kartodromo 25,53 233,24 119,43

Total 1442,44 728,75

Table 3: AGB vales per each zone expressed in Mg ha

-1

Zones

AGB (Mg 𝐡𝐚

𝟏

)

Argelia 30,96

Parque Lineal 19,41

Jipiro 25,94

Kartodromo 9,20

The total estimated AGB on the riverbanks that

cross the city and its parks was 2,864.34 Tn. Of the

totals mentioned, 1,442.44 Tn of AGB were

estimated in the areas where data were obtained,

while for the areas where survey were not performed

with the UAV, 1,421.90 Tn of AGB were estimated

for an area of 62.47 ha.

The validation of data taken in the field was

carried out for the H and DBH variables for a total of

54 trees, which were distributed in the plots and

included trees of different heights (from 9 to 25 m),

obtaining a higher r

value of 94%. These values

represent the error introduced in the measurement and

the error estimated by taking the data with the UAV,

where, being a passive sensor, it cannot penetrate the

Assessment of Aboveground Biomass-Vegetation Storage in Urban Centres Using Remote Sensing Technology

foliage of the vegetation or herbs or shrubs existing at

the foot of the recorded tree.

In order to compare the results of the two

methodologies corresponding to the use of satellite

images and data from a UAV, work has been done at

the plot level. In the results obtained at this level, the

data obtained by UAV in the Argelia area, the plot

that yielded a greater amount of AGB was plot 5, with

53.73 Tn of AGB. In the Parque Lineal zone, the plot

that yielded the greatest amount of AGB was plot 5,

with 22.33 Tn of AGB. In the Jipiro zone, plot 3 was

the one that yielded a greater amount of AGB, with

62.36 Tn of AGB, and in the Kartodromo zone, plot

1 was the one that yielded a greater quantity of AGB,

with 7.15 Tn of AGB.

On the other hand, in the satellite images in the

Argelia area, the plot that showed the highest value of

AGB was plot 5, with 55.14 Tn of AGB. In the Parque

Lineal area, in the 2019 satellite image, the highest

AGB value was obtained in plot 1, with 57.41 Tn of

AGB, and in the 2017 image in plot 2, with 67.43 Tn

of AGB. In the Jipiro area, in both satellite images,

the plot with the highest amount of AGB was plot 2,

with 87.20 Tn of AGB in the 2019 satellite image, and

with 73.05 Tn of AGB in the 2017 satellite image.

Finally, in the Kartodormo area in both satellite

images, the highest value of AGB calculated was

found in plot 5, with 78.18 Tn of AGB, recorded in

the 2019 satellite image, and with 62.27 Tn of AGB

in the satellite image of 2017.

The results obtained by plots reflect an evident

difference between the used methodologies. For this

analysis, the results were calculated as a percentage,

considering the AGB variable for this purpose. Thus,

from a total of 22 plots, it was obtained that only 4

plots presented a percentage difference between

methods of less than 51%; of these 4 plots, 2 showed

values of difference less than 7%. While of the other

18 plots with values greater than 51%, 5 plots

presented a percentage difference greater than 93%.

4 CONCLUSIONS

Based on the methodologies applied through the use

of remote sensing data, it is partially possible to

obtain estimates of aboveground biomass. This is due

to the fact that the results obtained through the use of

satellite images reflect oversaturated values, while the

estimation through the use of UAV presents values

based on detection at the individual tree level, using

the parameters of H, DBH and mean values of the

wood density.

The city of Loja has a low vegetation cover in

their urban area. As can be verified in the results

presented, the largest amount of vegetation exists on

the banks of the rivers. While in the parks where the

largest number of people and vehicles are

concentrated, the vegetation cover is low.

UAV technology allows products such as point

clouds to be obtained, as well as high-resolution

orthophotos. These GCP-assisted data can have very

good accuracies, which can be comparable with data

obtained with much more expensive platforms such

as those from LiDAR (Wilkes et al., 2018; Chen et

al., 2016). This lowers costs, and allows

investigations and monitoring to be carried out,

especially in small areas, where financial resources

are limited.

ACKNOWLEDGEMENTS

Thanks to the Universidad Técnica Particular de Loja

(UTPL) to facilitate this research by means of project

PY278, funded by the Smart Land initiative.

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Assessment of Aboveground Biomass-Vegetation Storage in Urban Centres Using Remote Sensing Technology