A novel nonintrusive soot diagnostics methodology was developed, validated and applied for in-situ determination of temperature, volume fraction and refractive index of soot aggregates formed inside flames by using near-infrared emission spectrometry. Research was conducted in three main parts, first one addressing development and validation of a comprehensive &quot / direct&quot / model for simulation of line-of-sight radiative emission from axisymmetric sooty flames by coupling sub-models for radiative transfer, radiative properties and optical constants. Radiative property estimation for soot agglomerates was investigated by experimentally validating discrete dipole approximation against microwave measurements and using it as reference to assess applicability of simpler Rayleigh-Debye-Gans approximation for fractal aggregates (RDG-FA). Comparisons between predictions of two methods for soot-like model aggregates demonstrated that radiative property predictions of RDG-FA are acceptably accurate for relatively small soot aggregates encountered in small-scale flames. Part two concerns experimental investigation of an axisymmetric ethylene/air diffusion flame by Fourier Transform Near-Infrared spectroscopy. Measurement of line-of-sight emission intensity spectra was performed along with analyses on calibration, noise, uncertainty and reproducibility. A noise characterization approach was introduced to account for spatial fluctuations which were found to dominate over spectral noise. Final part focuses on development, evaluation and application of an inversion methodology that inputs spectral emission intensity measurements from optically thin flames, removes noise, identifies soot refractive index from spectral gradients and retrieves soot temperature and volume fraction fields by tomographic reconstruction. Validation with simulated data and favorable application to measurements indicate that proposed methodology is a promising option for nonintrusive soot diagnostics in flames.

In this thesis work, temperature estimation algorithms based on physical and radiometric approaches are developed. Developed algorithms, firstly, tested on artificial images for different test cases. Following this, algorithms are tried out on real infrared images in order to verify that they are working properly. Finally, temperature estimations are done by including emissivity. Obtained results are compared to the temperature estimation results of a reference infrared camera. All the results and errors obtained during this study are presented and discussed.

The infrared atmospheric background modeling can be considered as one of the important key factor to develop a successful target detection technique. During the infrared atmospheric background modeling, defining the input parameters of the atmospheric profile are very important for the calculations of the absorption, emission and scattering effects of the atmosphere. The main objective of this thesis is to find the answer for the question &ldquo / is it possible to determine the &ldquo / effective&rdquo / height range for the sea level midlatitude clear weather conditions in the three special wavelength bands, 1-3 &amp / #61549 / m, 3-5 &amp / #61549 / m, 8-12 &amp / #61549 / m ?&rdquo / . The answer is important for three cases. These are to overcome the difficulties of finding all the parameters of the new atmospheric profile, to determine the dominant height range for the midlatitude region, and to shorten the time of the calculations of infrared background processes. In this study, it has been shown that it should be possible to determine the effective height range for sea level midlatitude clear weather conditions in the three special wavelength bands. As a result of this study it is shown that a new atmosphere model can be constructed more easily by overcoming the difficulties of finding all the parameters of the new atmospheric profile for the sea level clear weather midlatitude regions in a short time respectively. In this study the infrared radiation flux below 5 % difference between the whole, 100 km, and the effective height ranges is accepted.