Abstract:
Realistic scalable optical spectroscopic and multispectral imaging instrumentation platforms
as non-invasive optical diagnosis/detection systems have been developed and are presented in
this thesis. Wherever possible the state-of-the art optical and electronic instrumentation
techniques were employed in the development work, and the developed instruments have
been used in specific applications related to medicine, ecology and agriculture. Several
research and application tools have been designed and constructed under this project.
A detailed description is provided in the thesis with regard to the development and
commissioning of a GAs in Scattering Media Absorption Spectroscopy (GASMAS) setup,
which is the first of its kind built in Sri Lanka. GASMAS was used as a non-destructive
testing instrument for assessing the quality of the coating (an edible wax) which is sprayed for
preserving the freshness of paprika. For a good quality coating it has been found that, the time
constant for outward Oxygen diffusion of paprika was 58±5 h (even after 14 days of shelf
life). The main drawback of the GASMAS techniques is its inability to determine the absolute
optical path length.
A novel technique to measure the absolute optical path length using frequency modulated
continuous wave (FMCW) has been developed, which enables the estimation of path lengths
with the maximum accuracy of 14.3 %.
Application of chemometrics for point spectroscopic non-invasive investigation of
physiological maturity paprika using reflectance and florescence excited with the help of light
emitting diodes (LEDs) has also been carried out. It was revealed that the system can estimate
physiological maturity of different varieties of paprika up to 12 h.
In another development work, a web camera based diffused macroscopic red, green and blue
(RGB) imaging system has been designed and constructed, and this system was successfully
used to estimate the severity of cassava mosaic virus infestation, and to classify selected Sri
Lankan tomato varieties. The system was capable of discriminating senescence leaf from
severely infected cassava leaf. The imaging system was also found to be capable of sorting Sri
Lankan tomato varieties of Maheshi, Rajitha, T245 and Thilina with sensitivities of 93 %, 87
%, 42 % and 44 % respectively, and with specificities of 88 %, 90 %, 40 % and 38 %
respectively for up to three days after the plucking the fruits.
As a related development study, an LED based multimode microscopic system, as a research
tool, was also designed and constructed. The ability to analyze blood smears without staining
is one of the main advantages of this system. It was found that the system was capable of
discriminating oxyhemoglobin, deoxyhaemoglobin and Plasmodium falciparum parasites
(Malaria Parasites) in red blood cells.
A novel passive remote sensing technique was developed for bio aerosol (insect) monitoring.
As a related study, habitat of Calopteryx splendens and Calopteryx virgo were monitored with
the system. A total of 1,285 insect events passing the field of view were recorded in situ with
the system in a period of 12 h. Based on the analysis of these events it was possible to
differentiate male and female types of the insect of both varieties separately. The system also
successfully detected the interactions within and between sexes of the same species pertaining
to territorial behaviours and chasing of potential mates.