טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentEtzion Cohen Yael
SubjectRemote Sensing of Airborne Particulate Matter in Near
Ground Atmosphere by Nighttime Hyperspectral
Imaging
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor David Broday
Dr. Tzafrir Kolt
Professor Maxim Shoshany
Full Thesis textFull thesis text - English Version


Abstract

Urban scale ground remote sensing is a promising approach for monitoring fine ambient particulate matter (PM) at high spatiotemporal resolution. Current remote sensing methods for estimating aerosol optical thickness focus on vertical column observations of the entire atmosphere during daytime, and provide estimates of the aerosol optical thickness that are not easily related to ground level PM concentrations in vast regions of the world. A portable hyperspectral camera system that operates in the visible-near infrared  spectral range was used to develop a ground hyperspectral imaging methodology for spatiotemporal monitoring of fine PM concentrations along urban-scale open paths (line segments) under scarce natural illumination (e.g. nighttime).  Laboratory emulations of bimodal aerosols demonstrated the feasibility to acquire characteristic signatures and significant hyperspectral optical thicknesses for various combinations of fine particle modes. A genetic algorithm search was adjusted to retrieve modal concentrations, mostly resulting retrieval errors <5% for the laboratory experiments. A small scale environmental open path test demonstrated the need to use broad enough spectral information to enable accurate retrieval of modal concentrations. It was also found that coexisting fine size modes have mutual systematic effect on the retrieval accuracy. The hyperspectral imaging procedure was developed and demonstrated for a halogen illumination source. The capabilities and limitations of the source-sensor interactions and the geometrical effects of the imaging setup were studied under controlled (lab), stable (desert), and typical urban (Haifa) ambient conditions. The response of the hyperspectral sensor was found to be linear with the radiance, and the sensitivity limits of the system were estimated. The operational spectral range of the system was found to be limited to the 500-900 nm range. Error propagation analysis of the radiometric calibration revealed that PM variations that correspond to changes of 0.12-0.18 in the aerosol optical thickness should be discerned. This was confirmed by the hyperspectral camera response to controlled emissions of urban-like aerosols under environmental conditions. Response to high ambient PM loadings over 1 km urban open path was also clearly indicated. The open path limit of the developed procedure was found to be ~4 km, which provides a useful span for urban scale measurements. Such a suburban spatial resolution fits the requirements of modern environmental epidemiology studies, which are looking for better ways for assessing the exposure variability within the city.