Nghiên cứu điều chế alginate khối lượng phân tử thấp dùng làm thực phẩm chức năng hỗ trợ phòng chống đông máu tt tiếng anh

3 1.3 Differential Absorption LIDAR technique for measuring atmospheric ozone dítribution .... 6 1.3.5 DIAL measurement of ozone distribution in the lower atmosphere .... DESIGN AND SI

BỘ GIÁO DỤC VÀ ĐÀO TẠO VIỆN HÀN LÂM KHOA HỌC

VÀ CÔNG NGHỆ VIỆT NAM

HỌC VIỆN KHOA HỌC VÀ CÔNG NGHỆ

-Phạm Minh Tiến

NGHIÊN CỨU PHÂN BỐ OZONE TRONG KHÍ QUYỂN TẦNG THẤP VỚI ĐỘ PHÂN GIẢI CAO TRÊN CƠ SỞ PHÁT TRIỂN VÀ ỨNG DỤNG PHƯƠNG PHÁP LIDAR HẤP THỤ VI SAI

Chuyên ngành: Quang học

Mã số: 9 44 01 09

TÓM TẮT LUẬN ÁN TIẾN SĨ QUANG HỌC

Hà Nội, 2017

Công trình được hoàn thành tại Học Viện Khoa học và Công nghệ – Viện Hàn lâm Khoa học và Công nghệ Việt Nam

Người hướng dẫn Khoa học: PGS.TS Đinh Văn Trung

Phản biện 1:

Phản biện 2:

Luận án sẽ được bảo vệ trước Hội đồng đánh giá luận án tiến sĩ cấp Học Viện, họp tại Học Viện Khoa học và Công nghệ - Viện Hàn lâm Khoa hoc và Công nghệ Việt Nam vào hồi … giờ …, ngày … tháng… năm 201…

Có thể tìm hiểu luận án tại :

- Thư viện Học Viện Khoa học và Công nghệ

- Thư viện Quốc Gia Việt Nam

TABLE OF CONTENTS

PREFACE 1

1 The necessary of the thesis 1

2 Objectives of the thesis 1

3 The main research contents of the thesis 2

Chapter 1 INTRODUCTION 2

1.1 Ozone in the lower atmosphere 2

1.1.1 Formation and distribution 2

1.1.2 Ozone absorption cross section 3

1.1.3 Role and impact of atmospheric ozone 3

1.2 Measurement of atmospheric ozone 3

1.2.1 Overview 3

1.2.2 Measuring ozone in the atmospher 3

1.2.2.1 Total ozone measurements 3

1.2.2.2 Measurement of the vertical profile of ozone 3

1.3 Differential Absorption LIDAR technique for measuring atmospheric ozone dítribution 4

1.3.1 Physical principle of LIDAR and DIAL 4

1.3.2 LIDAR system and the LIDAR equation 4

1.3.3 Differential Absorption LIDAR technique 5

1.3.4 Wavelength selection for ozone measuring DIAL 6

1.3.5 DIAL measurement of ozone distribution in the lower atmosphere 6

1.3.6 Calculation of ozone concentration distribution 7

1.3.7 Accuracy of ozone DIAL measurement 7

Chapter 2 DESIGN AND SIMULATION OF A DIAL SYSTEM FOR MEASURING OZONE DISTRIBUTION IN THE

LOWER ATMOSPHERE 8

2.1 Design of a DIAL system for measuring ozone distribution 8

2.1.1 Diagram of Differential Absorption LIDAR 8

2.1.2 Optical transmitter 8

2.1.3 Optical receiver 8

2.1.4 Opto-electronic receiver 9

2.1.5 Processing and calculation program 9

2.2 Selection of pair of wavelength 9

2.3 Simulation of received backscattered DIAL signal 10

2.4 Simulation results and discussion 10

Chapter 3 DEVELOPMENT OF A DIFFERENTIAL ABSORPTIN LIDAR SYSTEM TO MEASURE ATMOSPHERIC OZONE DÍTRIBUTION 10

3.1 Configuration of DIAL system 10

3.2 Development of two DFDL 10

3.2.1 Oscillator 10

3.2.2 Optical pumping system 11

3.2.3 Optical amplifier 11

3.2.4 Active medium 12

3.2.5 Dye transfer pump 12

3.3 Development and evaluation of DIAL’s transmitter 12

3.4 Development of UV telescope and optical receiver 12

3.4.1 Development of UV telescope 12

3.4.2 Making a grinding and polishing machine 13

3.4.3 Development of optical receiver 13

3.5 Development of electronic receiver 13

3.6 Programming for signal acquirement and data processing 13

3.7 Testing of UV DIAL 14

Chapter 4 MEASUREMENT OFF OZONE DISTRIBUTION IN THE LOWER ATMOSPHERE 14

4.1 Data processing 14

4.2 Calculation of ozone concentration distribution 14

4.3 Results of vertical ozone distribution measurement 16

4.4 Error analysis 17

CONCLUSIONS 19

NEW CONTRIBUTIONS OF THE THESIS 20

LIST OF PUBLISHED ARTICLES 21

Preface

1 The necessary of the thesis

Ozone is of particular interest in the atmospheric composition because of its presence, distribution, and properties that greatly affect the life of our planet With higher concentrations in the stratosphere, ozone contributes greatly to protecting the earth by absorbing most of the dangerous ultraviolet radiation from the sun in a wavelength range

of 200 to 300 nm In the atmospheric layer close to the ground, although only a small component (about several tens of billions - ppb), but ozone is an important contributor to pollution smoke It is one of the main factors affecting human health, the life of organisms, and contributing to the greenhouse effect Therefore, the determination of the concentration and distribution of ozone in the atmosphere is essential, especially the atmosphere surrounding the ground

According to the report of the National Hydro-Meteorological Services of Vietnam (May, 2012), our country has about 20 Aero-Meteorological Observatories However, there are no annual atmospheric ozone monitoring data

The continuous monitoring of ozone concentration distribution will help predict and warn the air pollution to protect human health, increase our understanding of space weather and climate change, and build future development plans

2 Objectives of the thesis

Development of a UV Differential Absorption LIDAR ( DIAL) system for high resolution study of the distribution of ozone in the lower atmosphere

3 The main research contents of the thesis

The main content of the thesis is to develop an DIAL system with

two UV pulses emitted at wavelengths on (282.9 nm) and off (286.4

nm) into the atmosphere The elastic backscattering LIDAR signals of these radiations are acquired and their intensity is used to calculate the vertical ozone concentration The DIAL system includes:

Ozone (O3) is a pale blue gas and a powerful oxidant It has a distinctively pungent smell and strongly absorbs UV light [2,5] There is very little ozone in the earth's atmosphere, with an average of 10 million molecules of air per 3 molecules of ozone

1.1.1 Formation and distribution

Tropospheric ozone is produced from photochemical reactions with oxides of nitrogen (NOx) and volatile organic compound (VOC) molecules, in the presence of sunlight The highest ozone concentration tends to be concentrated in and around urban areas, where generate precursors necessary for ozone production, and often have peaks at noon and lowest at night Ozone concentration also vary from day to day depending on weather conditions, temperature, humidity, wind speed, etc

1.1.2 Ozone absorption cross section

The absorption cross section of ozone in the wavelength range from 200 to 1100 nm includes four absorption bands: Hartley, Huggins, Chappuis and Wulf Hartley và Huggins are intense bands

in UV region They are particularly important in atmospheric ozone monitoring using remote sensing techniques (Differential Optical Absorption Spectroscopy and Differential Absorption LIDAR)

1.1.3 Role and impact of atmospheric ozone

Stratospheric ozone filters out sunlight harmful UV wavelegths and protects the life on Earth In contrast, ozone in the lower atmosphere is a major component of photochemical smog in urban environments, an atmospheric pollutant, harmful to human health and

1.2.2 Measuring ozone in the atmosphere

1.2.2.1 Total ozone measurements

Total ozone is measured by remote‑sensing techniques using ground‑based and satellite instruments that measure irradiances in the

UV absorption spectrum of ozone between 300 and 340 nm

1.2.2.2 Measurement of the vertical profile of ozone

The vertical profile of ozone expresses ozone concentration as a function of height or ambient pressure It is measured with

ozonesondes, LIDARs, Umkehr technique with ground-based spectrometers and various satellite-borne instruments [19]

1.3 Differential Absorption LIDAR technique for measuring atmospheric ozone dítribution

1.3.1 Physical principle of LIDAR and DIAL

The main components of a LIDAR system consists of laser transmitter, optical receiver, electronic controller and software for processing and analyzing data

In LIDAR technique, laser radiation will interact with atmospheric components including molecules, atoms, aerosols and steam Then, the range of physical processes amenable to laser remote sensing includes Rayleigh scattering, Mie scattering, Raman scattering, resonance scattering, fluorescence, absorption, and differential absorption and scattering (DAS) These processes are responsible for the extenction of laser radiation beams emitted by LIDAR system

The absorbtion cross section of ozone in the ultraviolet region is much larger than the fluorescent cross section and Raman scattering cross section Therefore, the extinction of an appropriate laser beam caused by ozone will be a highly sensitive method to determine the concentration of ozone in the atmosphere

1.3.2 LIDAR system and the LIDAR equation

The functional elements and manner of operation of most lidar systems are schematically illustrated in Fig 1.17 An intense pulse of optical energy emitted by a laser is directed through some appropriate output optics toward the target of interest A small fraction of this pulse is sampled to provide a zero-time marker (trigger) The radiation

gathered by the optical receiver and the photodetection system The spectrum analyzer serves to select the observation wavelength interval and thereby discriminate against background ratiation at other wavelengths The Newtonian and Cassegrainian telescope are the main components in the optical receiver

Fig 1.17 The essential elements of a LIDAR system [3]

The detected LIDAR signal received from a distance R can be written as an equation, called the LIDAR equation:

𝑃(𝑅, 𝜆) = 𝑃0𝑐𝜏

2 𝐴𝜂𝑂(𝑅)

𝑅 2 𝛽(𝑅, 𝜆) 𝑒𝑥𝑝 [−2 ∫ 𝛼(𝑟, 𝜆)𝑑𝑟0𝑅 ] (1.21)

P 0 is the average power of a single laser pulse, τ is the temporal pulse

length The factor 1/2 appears because of an apparent “folding” of the

laser pulse through the backscatter process, c is the speed of light A

is the area of the primary receiver optics responsible for the collection

of backscattered light, and η is the overall system efficiency O(R) is the laser-beam receiver-field-of-view overlap function β(R,λ) is backscatter coefficient and α(R,λ) is the extinction coefficient The

factor 2 stands for the two-way transmission path

1.3.3 Differential Absorption LIDAR technique

Differential Absorption LIDAR technique allows the detection of atmospheric gases with high sensitivity With this technique, two

frequencies are used, one at the center of the absorption band (λon) and the other at the edge of the absorption band (λoff) By taking the ratio

of intensity Pon of lidar signal at wavelength λon and Poff signal at λoff, the concentration of interested gas is deduced from LIDAR equation

1.3.4 Wavelength selection for ozone measuring DIAL

In order to measure tropospheric ozone distribution where the ozone concentration is small, the wavelengths of laser transmitter must be selected in the strong absorption region of ozone, between

266 nm and 320 nm, to increase detection sensitivity

In addition, the selection of wavelengths results from the balance

of the following considerations: diferential absorption cross sections for optimizing the altitude range to make retrievals and the spatial resolution; reducing the impact of aerosol interference upon the ozone retrieval

1.3.5 DIAL measurement of ozone distribution in the lower

atmosphere

The DIAL measurements of ozone distribution in the lower atmosphere or the troposphere have used wavelength pairs in the range of 266 nm to 320 nm The DIAL systems have used the radiations emitted from a Q-switched frequency-quadruped Nd:YAG laser (266 nm); H2, D2, He Raman cells (Stokes lines: 289 nm, 299

nm, 316 nm) [48,49] or CO2 Raman cell (276.2 nm, 287.2 nm, 299.1) [50,51] pumped by a frequency-quadruped Nd:YAG at 266 nm; H2

Raman cell pumped by krypton–fluoride excimer laser at 248 nm (stimulated Raman shifting lines at 277 and 313 nm) [52]; or dye lasers [39,53,54] The altitude of measured ozone distribution in the troposphere of these DIAL systems depends on the pair of

wavelengths used, the intensity of the transmitter laser and the weather conditions

1.3.6 Calculation of ozone concentration distribution

LIDAR equation (1.22) of a elastic scattering differential

absorption LIDAR system is written for two wavelengths on and off

After taking the ratio of two intensities at two wavelengths, the

concentration of N (R) between the height R and R+R can be expressed as the sum of the measured signal term N s (R), the

differential backscattering term N b (R) and the differential

attenuation term N e (R) caused by atmospheric molecules, aerosols

and interference gases are as follows [3,39,58]:

𝑁𝑂3(𝑅) = 𝑁𝑠(𝑅) + 𝛿𝑁𝑏(𝑅) + 𝛿𝑁𝑒(𝑅) (1.31)

N S (R) is the basic term in (1.31), determined directly from the ratio of the signals The terms 𝛿𝑁𝑏(𝑅) và 𝛿𝑁𝑒(𝑅) are considered as correction terms, which must in some way be determined to determine

a more accurate ozone concentration The iterative method has been used to simultaneously determine the aerosol backscattering coefficient 𝛽𝑎𝑒𝑟(𝜆𝑜𝑓𝑓, 𝑅), the aerosol extinction coefficient

𝛼𝑎𝑒𝑟(𝜆𝑜𝑓𝑓, 𝑅), thereby determining 𝛿𝑁𝑏(𝑅), 𝛿𝑁𝑒(𝑅) and ozone concentration 𝑁𝑂3(𝑅) [39]

1.3.7 Accuracy of ozone DIAL measurement

The accuracy of a Differential Absorption LIDAR measurement

is determined by statistical errors Due to the random character of the signal detection process, the Poisson distribution has been assumed for the photon counting [37] The accuracy of the measurement depends on the approximations used to deduce the concentration of ozone and the linearity of the lidar signal

Chapter 2 Design and simulation of a DIAL system for measuring ozone distribution in the lower atmosphere 2.1 Design of a DIAL system for measuring ozone distribution

2.1.1 Diagram of Differential Absorption LIDAR

Fig 2.1 Diagram of Differential Absorption LIDAR system

2.1.2 Optical transmitter

Distributed Feedback Dye Laser (DFDL) was successfully developed at the Institute of Physics [67 – 72] With emitted power strong enough to be able to acquire LIDAR signals, DFDLs have a number of advantages: simple structure; large range of wavelength corrections (10-20 nm depending on the dye) and linewidth of ~ps So DFDL is convenient to select the pairs of wavelengths for the DIAL system, reduce the effect of interfering gas on the measurement results and give a high frequency doubling performance Therefore, the

DFDL has been selected to develop DIAL’s transmitter

2.1.3 Optical receiver

The main part of the DIAL’s receiver is a telescope The telescope

is designed and developed with a minimum diameter of 40 cm to increase the gain of LIDAR signals In addition, the aluminum must

be deposited on the surface of the telescope’s primary mirror so that