This document summarizes information about aerosols including their sources, sizes, health effects, measurement techniques, and a methodology for satellite aerosol retrieval. It discusses using MODIS data at 500m resolution to estimate aerosol optical thickness over Hong Kong and compares the results to AERONET ground measurements. Key steps in the methodology include calculating top-of-atmosphere reflectance, accounting for Rayleigh scattering, surface reflectance, gas transmissions, and atmospheric effects to derive aerosol reflectance and optical thickness.

1. PRESENT BY : MUHAMMAD FARIDZUL ADLI
BIN ZAKARIA
PRESENT BY : MUHAMMAD FARIDZUL ADLI
BIN ZAKARIA
Ahmad Mubin Wahab1 and Md. Latifur Rahman Sarker1, 2,*
1 Department of Geoinformation, Universiti Teknologi Malaysia,
Malaysia
2 Department of Geography and Environmental Studies,
University of Rajshahi, Bangladesh.
*Corresponding author: sarker@utm.my

3. 1.0 – INTRODUCTION

4. PM 2.5
PM 10
Atmospheric aerosol is a
suspension of liquid and
solid particles, with radii
varying from a few nm to
larger than 100 µm, in air.
Anthropogenic
Natural
Sources
WHAT IS
AEROSOL?
Sizes

5. Heart disease and
stroke
80%
Chronic obstructive
pulmonary disease
14%
Lung cancer
6%
0%
PREMATURE DEATH
1 - Human health Problems
asthma
hay fever
pulmonary
inflammation
respiratory symptoms
Cardiovascular
diseases1 – PM enters to
respiratory system 2/3 – PM 10
trapped in
respiratory system
4 – PM 2.5 penetrates
deep into lungs
AEROSOL EFFECTS

6. 2 - Visibility Degradation
Due to the extinction of light
when the light passing through
the atmosphere.
3 - Climate Change
Direct Effects
Indirect Effects
AEROSOL EFFECTS

7. Ground-based measurements Airborne-based measurements
Aerosol Robotic
Network
(AERONET)
Microstops II
Sunphotometer
Shipboard
measurement
Balloon Aircraft
Remote Sensing Satellite
Wide coverage Temporal resolution
Good spatial
information
Requires high spatial and temporal
resolution of data because of the short
life span of aerosol (7 to 10 days).
AEROSOL
MEASUREMENT

8. SATELLITE AEROSOL RETRIEVAL MECHANISM
Rayleigh reflectance
(𝝆 𝐑𝐚𝐲) + Aerosol
reflectance
Surface Reflectance (𝝆 𝒔𝒖𝒓𝒇)
Top of Atmosphere
Reflectance (𝝆 𝐓𝐎𝐀)
𝝆 𝐓𝐎𝐀 = 𝝆 𝐀𝐞𝐫 + 𝝆 𝐑𝐚𝐲 + 𝝆 𝒔𝒖𝒓𝒇
 The key factor of the aerosol retrieval is to estimate surface reflectance
that attempts to differentiate the aerosol signal from surface.
𝝆 𝐀𝐞𝐫 = 𝝆 𝐓𝐎𝐀 − 𝝆 𝐑𝐚𝐲 − 𝝆 𝒔𝒖𝒓𝒇

9. PROBLEM & SIGNIFICANT
MODIS Local Scale Aerosol
 Low spatial resolution (10 km)
 Lots of missing pixels
 No real-time data available
High Resolution (500 m)
Real-time data available
Good spatial distribution
Based on the local
aerosol model

10.  To compare the potential of two different
AOT algorithms,
 To determine which technique can provide
effective aerosol retrieval estimation.

11. STUDY AREA
 One of the most densely populated area.
 7 million people living in 1104 km2 of land areas.
Availability of Long-term
Ground data measurement
(AERONET station).
Several studies have already
been conducted.
One of the most polluted
urban areas in the world.
Availability of Long-term
Ground data measurement
(AERONET station).
Several studies have already
been conducted.
One of the most polluted
urban areas in the world.
Why Hong Kong?

12. DATA USED
MOD02HKM MOD03 MOD09GA
Aerosol Robotic
Network
(AERONET)
• MOD02HKM - swath data with calibrated radiance at 500m.
• MOD03 - Geolocation data (geodetic coordinates, ground
elevation, solar zenith angle, solar azimuth angle, satellite
zenith angle and satellite azimuth angle).
• MOD09GA - Land surface reflectance product at 500m.
• MOD05 - Total Water Vapour content.
• MOD07 - Total Ozone Content.
• MOD021KM – Channel 26 (cirrus reflectance).
• Additionally, MODIS aerosol level 2 collection 005 (MOD04 L2
C005) was used to compare with our result.
• AERONET Level 1.5 data was used for the validation.

13. 2.0 – METHODOLOGY

14. OVERALL METHODOLOGY

15. AEROSOL REFLECTANCE (𝜬 𝐀𝐞𝐫)
TOA
REFLECTANCE
RAYLEIGH
REFLECTANCE
SURFACE
REFLECTANCE
TOTAL
TRANSMISSION OF
WATER VAPOUR
TOTAL
TRANSMISSION OF
OZONE GAS
𝜬 𝐀𝐞𝐫 𝛌,𝜽 𝒔,𝜽 𝒗,𝝓 =
𝝆 𝐓𝐎𝐀 𝛌,𝜽 𝒔,𝜽 𝒗,𝝓
𝑻 𝒈 𝑴, 𝑼 𝑶 𝒈
𝑻 𝑶 𝟑
𝑴, 𝑼 𝑶 𝟑
− 𝝆 𝐑𝐚𝐲 𝛌,𝜽 𝒔,𝜽 𝒗,𝝓 –
𝑻 𝒂𝒕𝒎 𝜽 𝒔,𝜽 𝒗
𝝆 𝐬 𝛌,𝜽 𝒔,𝜽 𝒗,𝝓 𝑻 𝑯 𝟐 𝑶
𝒃
𝑴, 𝑼 𝑯 𝟐 𝑶
𝟏 − 𝝆 𝐬 𝛌,𝜽 𝒔,𝜽 𝒗,𝝓 𝝆 𝑯𝒆𝒎
𝑻 𝑯 𝟐 𝑶
𝒂
𝑴,
𝑼 𝑯 𝟐 𝑶
𝟐
TOTAL
TRANSMISSION OF
OTHER GAS
TOTAL
ATMOSPHERIC
TRANSMISSION
HEMISPHERIC
REFLECTANCE

16. TOA REFLECTANCE
𝒅 =
𝟏
(𝟏+𝟎.𝟎𝟑𝟑𝐜𝐨𝐬(𝑫𝑶𝒀
𝟐𝝅
𝟑𝟔𝟓
)
satellite receives TOA spectral radiance 𝐿 𝑇𝑂𝐴 𝜆 was normalized to the
solar illumination condition for each wavelength to generate TOA
spectral reflectance using the equation as follows:
Band Wavelength (µm) ESUN (Wm-2 μm-1)
1 0.646 1596
2 0.855 974.7
3 0.466 2017
4 0.553 1850
5 1.243 463.1
6 1.632 232.9
7 2.119 92.67
𝒅 is earth-sun distance can
be calculated as following:
𝒅 is earth-sun distance can
be calculated as following:
𝝆 𝑻𝑶𝑨 𝝀 =
𝝅𝑳 𝑻𝑶𝑨 𝝀 𝒅 𝟐
𝑬𝒔𝒖𝒏 𝝀 ∗ 𝒄𝒐𝒔𝜽 𝒔
Source : MODIS Science Team
DOY – Julian daysDOY – Julian days
𝜽 𝒔 is solar zenith angle,𝜽 𝒔 is solar zenith angle,
𝑬 𝟎 is extraterrestrial solar
irradiance,
𝑬 𝟎 is extraterrestrial solar
irradiance,
where, 𝑳 𝑻𝑶𝑨 𝝀 is TOA
spectral radiance obtained
from MOD02HKM data.
where, 𝑳 𝑻𝑶𝑨 𝝀 is TOA
spectral radiance obtained
from MOD02HKM data.

17. 𝑷 𝑹𝒂𝒚 𝝀 =
𝝉 𝑹𝒂𝒚 𝝀 . 𝝆 𝑹𝒂𝒚
𝟒(𝒄𝒐𝒔𝜽 𝒔. 𝒄𝒐𝒔𝜽 𝒗)
RAYLEIGH
REFLECTANCE (𝑷 𝑹𝒂𝒚)
where, 𝑐𝑜𝑠𝜃𝑠 is cosine solar zenith
angle, and 𝑐𝑜𝑠𝜃 𝑣 is cosine sensor
zenith angle.
where, 𝑐𝑜𝑠𝜃𝑠 is cosine solar zenith
angle, and 𝑐𝑜𝑠𝜃 𝑣 is cosine sensor
zenith angle. 𝝉 𝐑𝐚𝐲 𝛌 = 𝒂. 𝛌− 𝒃+𝒄𝛌+ 𝐝 𝛌
. 𝐞𝐱𝐩 − 𝒛 𝟖. 𝟓
Constant 0.2 – 0.5 µm > 0.5 µm
a 3.01577 x 10-28 4.01061 x 10-28
b 3.55212 3.99668
c 1.35579 1.10298 x 10-3
d 0.11563 2.71393 x 10-2
)𝜸 = 𝜹 ( 𝟐 − 𝜹
Ɵ is scattering
phase angle
Ɵ is scattering
phase angle
Ɵ = 𝒄𝒐𝒔−𝟏
(−𝒄𝒐𝒔𝜽 𝒔 𝒄𝒐𝒔𝜽 𝒗 + 𝒔𝒊𝒏𝜽 𝒔 𝒔𝒊𝒏𝜽 𝒗 𝝓
Wavelength (µm) 𝛅 𝛄
0.466 0.02899 0.01471
0.553 0.02842 0.01442
0.646 0.02786 0.01413
Source : Butcholtz, 1995
Source : Butcholtz, 1995
𝜹 is depolarization factor𝜹 is depolarization factor
𝒛 is elevation𝒛 is elevation 𝒂, 𝒃, 𝒄, 𝑎𝑛𝑑 𝒅 𝑖𝑠 𝑅𝑎𝑦𝑙𝑒𝑖𝑔ℎ
𝑠𝑐𝑎𝑡𝑡𝑒𝑟𝑖𝑛𝑔 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡
𝒂, 𝒃, 𝒄, 𝑎𝑛𝑑 𝒅 𝑖𝑠 𝑅𝑎𝑦𝑙𝑒𝑖𝑔ℎ
𝑠𝑐𝑎𝑡𝑡𝑒𝑟𝑖𝑛𝑔 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡
𝝉 𝑹𝒂𝒚 𝝀 is Rayleigh optical depth𝝉 𝑹𝒂𝒚 𝝀 is Rayleigh optical depth
𝝆 𝑹𝒂𝒚 =
𝟑
𝟒 𝟏 + 𝟐𝜸
[ 𝟏 + 𝟑𝜸 + 𝟏 − 𝜸 𝒄𝒐𝒔 𝟐Ɵ
𝝆 𝑹𝒂𝒚 is Rayleigh phase function𝝆 𝑹𝒂𝒚 is Rayleigh phase function

18. Total Atmospheric Transmission (𝑻 𝒂𝒕𝒎)
𝑻 𝒂𝒕𝒎(𝜽 𝒔,𝜽 𝒗) = 𝑻 𝒂𝒕𝒎(𝜽 𝒔). 𝑻 𝒂𝒕𝒎 𝜽 𝒗
𝑻 𝒂𝒕𝒎(𝜽) = 𝑻 𝑹𝒂𝒚(𝛉) . 𝑻 𝒂𝒆𝒓(𝛉)
𝑻 𝑹𝒂𝒚(𝛉) = 𝒆𝒙𝒑(−𝜷 𝑹𝒂𝒚 . 𝝉 𝑹𝒂𝒚 . (𝟏/𝒄𝒐𝒔𝜽)) 𝑻 𝒂𝒆𝒓(𝛉) = 𝒆𝒙𝒑(−𝜷 𝒂𝒆𝒓. 𝝉 𝒂𝒆𝒓 . (𝟏/𝒄𝒐𝒔𝜽))
𝜷 𝑹𝒂𝒚 =
𝒊=𝟏
𝟓
𝒃𝒊
𝑹𝒂𝒚
. (𝟏/𝒄𝒐𝒔𝜽)−(𝒊−𝟏) 𝜷 𝑨𝒆𝒓 =
𝒊=𝟏
𝟓
𝒃𝒊
𝒂𝒆𝒓
. (𝟏/𝒄𝒐𝒔𝜽)−(𝒊−𝟏)
Coefficient Rayleigh Aerosol
𝒃 𝟏 -0.44408 0.01176
𝒃 𝟐 4.49481 1.01682
𝒃 𝟑 -9.71368 -2.32949
𝒃 𝟒 9.49795 2.11831
𝒃 𝟓 -3.42016 -0.71737
Total Rayleigh Transmission (𝑻 𝑹𝒂𝒚(𝛉) ) Total Aerosol Transmission (𝑻 𝒂𝒆𝒓(𝛉) )
Source : Hoyningen-Huene et al., 2007

19. SURFACE REFLECTANCE (𝜌𝑠)
An improvement of DDV techniques (more robust)
Empirical relationship (nonlinear relationship) between
visible channel and SWIR channel.
Calibrated by refining atmospheric correction algorithm
(6SV code).
An improvement of DDV techniques (more robust)
Empirical relationship (nonlinear relationship) between
visible channel and SWIR channel.
Calibrated by refining atmospheric correction algorithm
(6SV code).
𝐌𝐎𝐃𝟎𝟗𝐆𝐀
https://lpdaac.usgs.gov/dataset_discovery/modis/modis_products_table/mod09ga

20. 𝑼 𝑶 𝟑 − the total ozone content
(obtained from the MOD07 level 2).
𝑴 − air mass factor (𝑴 =1/𝒄𝒐𝒔𝜽).
𝒌 𝑶 𝟑 − weighting coefficient of ozone
gases (derived from 6SV code).
𝑻 𝑶 𝟑
(𝑴, 𝑼 𝑶 𝟑) = 𝒆−𝑴𝒌 𝑶 𝟑 𝑼 𝑶 𝟑
𝑼 𝑯 𝟐 𝑶 − total water vapour content (obtained from MOD05 level 2) .
𝑴 −air mass factor (𝑴 =1/𝒄𝒐𝒔𝜽). .
𝒌 𝑯 𝟐 𝑶
𝟏
, 𝒌 𝑯 𝟐 𝑶
𝟐
, and 𝒌 𝑯 𝟐 𝑶
𝟑
− weighting coefficients of water vapour (derived from 6SV code)
Total transmission of other gases
(𝑪𝑶 𝟐 𝒂𝒏𝒅 𝑵 𝟐 𝑶)
• Only for the wavelength at 2.119 µm.
• Obtained directly from 6SV code using the
standard atmosphere model.
Wavelength (µm) Gas Absorption Effect
0.466 O3
0.553 O3
0.646 O3 and 𝐻2 𝑂
2.119 𝐻2 𝑂, CO2 and N 𝟐O
Total Gaseous Transmission
Total transmission of ozone gas (𝑇 𝑂3
)
Total gaseous transmission of water vapour (𝑇 𝐻2 𝑂)
𝑻 𝑯 𝟐 𝑶 𝑴, 𝑼 𝑯 𝟐 𝑶 = 𝒆𝒙𝒑[𝒌 𝑯 𝟐 𝑶
𝟏
𝑴𝑼 𝑯 𝟐 𝑶 + 𝒌 𝑯 𝟐 𝑶
𝟐
𝑳𝒐𝒈(𝑴𝑼 𝑯 𝟐 𝑶) + 𝒌 𝑯 𝟐 𝑶
𝟑
𝑴𝑼 𝑯 𝟐 𝑶 𝑳𝒐𝒈(𝑴𝑼 𝑯 𝟐 𝑶)]

21. Hemispheric reflectance
 𝛕 𝐚𝐭𝐦 is atmospheric optical
depth (𝛕 𝐑𝐚𝐲 + 𝛕 𝐚𝐞𝐫).
 𝐛𝐢 is polynomial coefficients
of hemispheric reflectance.
 𝛕 𝐚𝐭𝐦 is atmospheric optical
depth (𝛕 𝐑𝐚𝐲 + 𝛕 𝐚𝐞𝐫).
 𝐛𝐢 is polynomial coefficients
of hemispheric reflectance.
𝝆 𝑯𝒆𝒎 =
𝒊=𝟏
𝟒
𝒃𝒊 . 𝝉 𝒂𝒕𝒎
𝒊 Coefficient
Hemispheric
Reflectance
𝒃 𝟏 0.33185
𝒃 𝟐 -0.19653
𝒃 𝟑 0.08935
𝒃 𝟒 -0.01675
Source : Hoyningen-Huene et al., 2007
 Integral of the bidirectional reflectance distribution function
(BRDF) over all viewing directions.
 Crucial for surface function correction due to multiple scattering
effect.
 Has a high influence on the bright surfaces, while less over low
surface reflectance.
 Integral of the bidirectional reflectance distribution function
(BRDF) over all viewing directions.
 Crucial for surface function correction due to multiple scattering
effect.
 Has a high influence on the bright surfaces, while less over low
surface reflectance.

22. LOCAL AEROSOL MODEL CHARACTERIZATION
Identify number of cluster (k)Identify number of cluster (k)
VRC methodVRC method Ward’s methodWard’s method
Clustering Analysis
K-means clustering analysis
Local Aerosol Model
K-means
clustering
ANOVA Tables
Sum of F-test
values (𝑉𝑅𝐶 𝑘)
𝝎 𝒌 = 𝑽𝑹𝑪 𝒌+𝟏 − 𝑽𝑹𝑪 𝒌 − 𝑽𝑹𝑪 𝒌 − 𝑽𝑹𝑪 𝒌−𝟏
Number of cluster (k)
(smallest value of 𝜔 𝑘)
Hierarchical
cluster analysis
Agglomerative
procedures
Ward’s method
Elbow rule
Number of cluster (k)
-based on the number of
step has biggest jump.

23. AOT RETRIEVE USING SBDART CODE
MODIS Aerosol
Reflectance
(0.466 µm, 0.553 µm,
and 0.646 µm)
Local Aerosol
Model parameters
SBDART code
Variables No. Parameters
Wavelength 3
0.466 µm, 0.553 µm,
and 0.646 µm
AOT at
0.55 µm
9
0.0, 0.2, 0.4, 0.8,
1.4, 1.8, 2.2, 3.0,
and 5.0
SZA 9 0º ~ 80 º, Δ = 10 º
VZA 17 0º ~ 80 º, Δ = 5 º
PHI 18 0º ~ 170 º, Δ = 10 º
Aerosol
Model
4
SSA, Qext, and g at
0.439 µm, 0.676 µm,
0.869 µm, and 1.02
µm.
TOA Reflectance as
a function of AOT
Aerosol Reflectance
as a function of AOT
Interpolation
(Optimal
spectral
shape-fitting
technique)
No
AOT (0.466 µm, 0.553
µm, and 0.646 µm)
AOT at 0.55 µm
Yes
𝑥2
=
1
𝑛
𝑖=1
𝑛
𝜌 𝐴𝑒𝑟
𝑚
λ𝑖 − 𝜌 𝐴𝑒𝑟
𝑐
λ𝑖
𝜌 𝐴𝑒𝑟
𝑚
λ𝑖
2
𝑥2
=
1
𝑛
𝑖=1
𝑛
𝜌 𝐴𝑒𝑟
𝑚
λ𝑖 − 𝜌 𝐴𝑒𝑟
𝑐
λ𝑖
𝜌 𝐴𝑒𝑟
𝑚
λ𝑖
2
ρAer(λ) = ρTOA λ − ρRay λ

24. AOT RETRIEVE USING DIRECT RETRIEVAL
MODIS Aerosol
Reflectance
(0.466 µm, 0.553 µm, and
0.646 µm)
Local Aerosol
Model parameters
MIEV Code
Aerosol Phase
Function as a
function of
Scattering Angle
Interpolation
(linear) with
MODIS scattering
angle
AOT at 0.55 µm
(model 1)
AOT at 0.55 µm
(model 2)
AOT at 0.55 µm
(model 3)
AOT at 0.55 µm
(model 4)
Legendre
coefficient 𝒑 𝛉 =
𝒏=𝟎
∞
𝟐𝒏 + 𝟏 . 𝒌 𝒏. 𝑷 𝒏 𝝁
𝝁 − cosine scattering
angle.
𝒌 𝒏 − n-th Legendre
coefficient.
𝑷 𝒏 − n-th order of
Legendre polynomial.
AOT retrieval
𝜏 𝑎𝑒𝑟 𝜆 =
4𝜇 𝑠 𝜇 𝑣 𝑃𝑎𝑒𝑟 𝜆
𝜔 𝑜 𝑝 θ
Ref. ind. real and
imaginary, and effective
radius at 0.439 µm,
0.676 µm, 0.869 µm, and
1.02 µm

25. 3.0 – RESULT &
DISCUSSION

26. VALIDATION OF MODIS AOT 500 M USING AOT FROM
AERONET STATION
R = 0.48
RMSE = 1.47
R = 0.48
RMSE = 1.47
R = 0.86
RMSE = 0.56
R = 0.86
RMSE = 0.56
R = 0.89
RMSE = 0.09
R = 0.89
RMSE = 0.09
SBDARTSBDART
Direct Model -1Direct Model -1 Direct Model -2Direct Model -2
R = 0.74
RMSE = 0.99
R = 0.74
RMSE = 0.99
Direct Model -3Direct Model -3
R = 0.77
RMSE = 0.81
R = 0.77
RMSE = 0.81
Direct Model -4Direct Model -4

27.  Low accuracy against AERONET
AOT.
 The accuracy varies with local
aerosol models.
 It is because an improper account to
molecular effects in RT calculation
(Kokhanovsky & de Leeuw, 2009).
 Low accuracy against AERONET
AOT.
 The accuracy varies with local
aerosol models.
 It is because an improper account to
molecular effects in RT calculation
(Kokhanovsky & de Leeuw, 2009).
 High accuracy against AERONET
AOT.
 Provide AOT with better
performance and less error.
 It is because of RT code has the
ability to solve the complexity of RT
equations with rigorous computation
in order to minimize substantial error
(Kokhanovsky and de Leeuw, 2009).
 High accuracy against AERONET
AOT.
 Provide AOT with better
performance and less error.
 It is because of RT code has the
ability to solve the complexity of RT
equations with rigorous computation
in order to minimize substantial error
(Kokhanovsky and de Leeuw, 2009).
DISCUSSION
SBDART code Direct retrieval

28. MODIS AOT 500 M VS MODIS AOT PRODUCT
MODIS AOT 500 M VS AERONET AOTMODIS AOT PRODUCT VS AERONET AOT
R = 0.94
RMSE = 0.09
R = 0.94
RMSE = 0.09
R = 0.90
RMSE = 0.11
R = 0.90
RMSE = 0.11

29. AOT Spatial Distribution
Comparison of spatial distribution of MODIS
AOT 500 m and MODIS AOT product
MODIS AOT 500 m
 Good spatial information
and high spatial resolution
(500 m).
 No missing pixels are
detected.
 Poor spatial information and
lower spatial resolution (10
km).
 lot of missing pixel especially
in urban and industrial areas.
 Due to bright pixels was
discarded in the retrieval
algorithm.
MODIS AOT product (10 km)

30. 4.0 – CONCLUSION

31. CONCLUSION
 MODIS AOT generated from SBDART code (RT code)
agrees very well with the AOT from AERONET
measurement.
 It showed better accuracy and small error compared to
MODIS AOT generated from direct approach.
 Considering the reasonable accuracy, high spatial
resolution and good spatial distribution, it can be
concluded AOT is possible to be estimated from MODIS
500m using RT code.
 MODIS AOT generated from SBDART code (RT code)
agrees very well with the AOT from AERONET
measurement.
 It showed better accuracy and small error compared to
MODIS AOT generated from direct approach.
 Considering the reasonable accuracy, high spatial
resolution and good spatial distribution, it can be
concluded AOT is possible to be estimated from MODIS
500m using RT code.