Phan D. Dao

Polarimetric wavelet phenomenology of space materials

This paper describes new polarimetric wavelet detection principles applied to the backscattering characteristics of space materials in the near infrared. Efficient polarimetric detection techniques are combined with cross-correlation and wavelet analysis for enhanced characterization of space materials. The outcome of this study will support remote characterization of space materials and structures with enhanced discrimination, localization, and high-dynamic range while maintaining uncompromised sensitivity.

Infrared photon discrimination of lung cancer cells

The objective of this study is to explore the polarimetric phenomenology of near infrared light interaction with healthy and lung cancer monolayer cells by using efficient polarimetric transmission detection techniques. Preliminary results indicate that enhanced discrimination between normal and different types of lung cancer cell stages can be achieved based on their transmitted intensities and depolarization properties of the cells. Specifically, the sizes of the nuclei of the cancer cells and the nucleus-to-cytoplasmic ratios appear to have potential impact on the detected polarimetric signatures leading to enhanced discrimination of lung cancer cells.

Object detection and characterization by monostatic ladar Bidirectional Reflectance Distribution Function (BRDF) using polarimetric discriminants

The purpose of this study is to explore novel monostatic ladar detection principles utilizing polarimetric Bidirectional Reflectance Distribution Function (BRDF) and single-pixel detection parameters. The depolarization of backscattered elliptical polarized light beams, from extended area space materials, was studied at different sample orientations. Specifically, the depolarization ratio for both linearly and circularly polarized light waves was estimated under quasimonostatic transceiver geometry. The experimental results indicate that space object materials exhibit distinct depolarization signatures, which provide enhanced discrimination capabilities. The outcome of this study would enhance the monostatic-ladar detection and discrimination capabilities.

Superresolution Multispectral Imaging Polarimetric Space Surveillance LADAR Sensor Design Architectures

This study consists of the exploitation of novel ladar design principles and architectures aimed at the increasing of the superresolution, and imaging capabilities of the space surveillance ladars for efficient detection, discrimination, and monitoring of space objects and man-made materials detection. Ladar interferometric techniques relying on Vertical- Cavity Surface-Emitting Laser (VCSEL) coherent arrays would provide enhanced lightweight imaging solutions, with unsurpassable dynamic range, at low power consumption, remarkable reliability, and reduced cost. The experimental results of this study indicate that the signal-to-noise ratio of backscattered optical signals can be enhanced significantly, by utilizing efficient single-pixel polarimetric techniques; as a result the ladar range accuracy would be improved significantly. In addition, several space materials and man-made materials are shown to exhibit distinct depolarization signatures which can be used to characterize, classify, and identify those materials.

Polarimetric wavelet fractal remote sensing principles for space materials

A new remote sensing approach based on polarimetric wavelet fractal detection principles is introduced and the Mueller matrix formalism is defined, aimed at enhancing the detection, identification, characterization, and discrimination of unresolved space objects at different aspect angles. The design principles of a multifunctional liquid crystal monostatic polarimetric ladar are introduced and related to operating conditions and system performance metrics. Backscattered polarimetric signal contributions from different space materials were detected using a laboratory ladar testbed, and then analyzed using techniques based on wavelets and fractals. The depolarization, diattenuation, and retardance of the materials were estimated using Mueller matrix decomposition for different aspect angles. The outcome of this study indicates that polarimetric fractal wavelet principles may enhance the capabilities of the ladar to provide characterization and discrimination of unresolved space objects.

Characterization of particles from stratospheric launch vehicle plumes using wavelength‐dependent lidar techniques

Our Mobile Lidar Trailer (MLT) has been deployed to Cape Canaveral Air Station for the purpose of studying the characteristics of launch vehicle plumes in the stratosphere. In addition to measurements of plume extent and dispersion rates, information on particle species and size can be obtained from the wavelength dependence of the Mie return signal. We measure the backscattering ratio of Mie to Rayleigh return at several wavelengths and compare the results to a model of Mie scattering cross sections for homogeneous spheres of specific refraction index and radius. Of primary interest are the calculations for particles which are present in the exhaust of solid rocket motors (SRM) and are conjectured to be instrumental in the catalysis of halogenic destruction of stratospheric ozone. Our data indicate that these particles, at least within the first half-hour after launch, are small (r < 50 nm as an upper limit). The data also shows a trend of the mean particle radius increasing with time.

Development of a deployable aerosol/water vapor lidar to characterize the atmosphere

A trailer-based lidar, named Humidity and Aerosol Lidar (HAL), is being built as a remote sensing tool to characterize atmospheric aerosol and water vapor in the line-of-sight. Water vapor and aerosol in the lower atmosphere are critical components affecting the propagation of high-energy laser beams and microwave. The sensor is developed to collect high temporal and vertical resolution data of atmospheric aerosols and water vapor. This ground-based system also serves as a demonstration and an engineering study of a flight-capable sensor for real-time diagnostic of the atmosphere. The lidar, operating on the principles of differential absorption, could measure water vapor to 10 km altitudes. It also measures aerosols and cloud backscatter at altitudes up to 18 km and ranges up to 90 km. Operating with a hemispherical scanner, the sensor could map the 3-dimensional field of aerosols and water vapor and provide vertical as well as horizontal structures. A unidirectional Alexandrite ring laser, operating in single mode near 727.49 nm, is the laser source. The sensor is designed to operate in day and night time. A description of the system, its wavelength calibration unit, the transmitter-receiver system and projected performance will be discussed. Results of the photo-acoustic calibration cell and wavelength selections will be presented. Preliminary results of water vapor and aerosols will be discussed.

Density Measurements With Combined Raman-Rayleigh Lidar

A combined Raman-Rayleigh Lidar (Light Detection And Ranging) has recently been implemented at the Air Force Geophysics Laboratorys ground-based lidar station to measure neutral density from the lower stratosphere to the upper mesosphere. Rayleigh Lidar reliably measures relative densities in the region above 30 km. In this region, atmospheric extinction can be neglected and backscattering is primarily due to Rayleigh scattering. However, when density measurements are needed for the lower stratosphere two complications arise: the contribution of aerosol (Mie and Rayleigh) scattering to the Rayleigh signal and the effect of aerosol attenuation. Vibrational Raman scattering, being an elastic process for molecules only, can be used to resolve the first ambiguity. The second difficulty requires an inversion technique to help determine the attenuation profile from the Lidar signal and provide a transmission correction of this signal. For the lower stratosphere, the technique adopted in this laboratory is a three-step treatment of data. In step (1) Klett inversion is applied on the elastic scattering signal (Mie and Rayleigh) to obtain a transmission altitude profile. In step (2) the molecular signal from the Raman Lidar is corrected for atmospheric attenuation. In step (3), Raman data for below 25 km is spliced to Rayleigh data for above 25 km to give the entire profile of neutral density. Application of this analysis to experimental data will be shown and discussed.

An automated ladar polarimetric system for remote characterization of space materials

The calibration, testing, and operational principles of an efficient multifunctional monostatic polarimetric ladar are introduced and related to the system performance metrics. The depolarization, diattenuation, and retardance of the materials were estimated using Mueller matrix (MM) decomposition for different aspect angles. The outcome of this study indicates that polarimetric principles may enhance the capabilities of the ladar to provide adequate characterization and discrimination of unresolved space objects.

Improved correlation determination for intensity interferometers

To image astronomical objects, the Hanbury Brown Twiss (HBT) technique involves measuring intensity correlation for an array of telescopes. The correlation of the intensity fluctuations is a measure of the magnitude of the coherence and can be used to retrieve the intensity distribution of the source using the Van Cittert-Zernike theorem. For low spectral irradiance sources, coincidence counting using modern techniques can drastically reduce data storage/processing requirements as well as allowing for optimization of the effective SNR bandwidth. In counting Intensity Interferometry (II), count fluctuations are measured instead of intensity fluctuations as with an analog II. Those are the two II techniques currently reported in the literature. Since the successful width measurements of bright stars by HBT in the 70s, advances in detectors promise opportunities to apply II to dimmer non-point source objects. To improve SNRs, we propose a new data processing technique for measuring correlation in the low light regime that ensures maximum bandwidth allowed by the reproducibility of photon pulses.