<p> A lightning interferometer is an instrument which determines the direction to a lightning-produced radio point source by correlating the signal received at two or more antennas. Such instruments have been used with great success for several decades in the study of the physical processes present in a lightning flash. However, previous instruments have either been sensitive to only a narrow radio bandwidth so that the correlation can be done using analog hardware, or have been sensitive to a wide bandwidth but only recorded a short duration of the radiation produced by a lightning flash. </p><p> In this dissertation, a broad bandwidth interferometer is developed which is capable of recording the VHF radio emission over the entire duration of a lightning flash. In order to best utilize the additional data, the standard processing techniques have been redeveloped from scratch using a digital cross correlation algorithm. This algorithm can and does locate sources as faint as the noise level of the antennas, typically producing 100,000 or more point source locations over the course of a lightning flash. </p><p> At very low received power levels, the likelihood that a signal received at the antenna will be affected by the environmental noise is substantially higher. For this reason, the processing allows for the integration windows of the cross correlation to be heavily overlapped. In this way, the location of each event can be based on a distribution of windows. Further, noise identification techniques which leverage the heavily overlapped windows have been developed based on: the closure delay, the standard deviation, the correlation amplitude, and the number of contributing windows. The filtration techniques have proven to be very successful at identifying and removing mis-located sources, while removing the minimum number of low amplitude sources which are well located. </p><p> In the past, lightning interferometers have been limited to using only two perpendicular baselines to determine the direction to each point source. Additional techniques are developed in this dissertation for efficiently computing the image of a point source in the sky using an arbitrary number of antennas in an arbitrary configuration. The multiple baseline techniques further improves the sensitivity and accuracy of the locations provided by broadband interferometers. </p><p> To demonstrate the usefulness of broadband interferometers, the activity of 6 flashes spanning a diverse selection of lightning flash types are examined in this dissertation. This includes detailed analysis of negative stepped leaders, positive un-stepped leaders, K-changes, and fast positive breakdown. Initial breakdown pulses which are seen at the beginning of the flash are found to be no different than horizontal negative leader steps seen later in the flash. Evidence is found that positive leaders produce VHF radiation, as opposed to all of the radiation in the positive breakdown region being produced by retrograde negative breakdown. The time resolved three-dimensional velocity of 47 K-changes occurring in two flashes is measured. And finally, fast positive breakdown is characterized and found to be produced by a positive streamer process instead of a leader process. </p><p> Observations made with the instrument showcase the capabilities of a continuous sampling broadband interferometer. The instrument makes possible measurements which were difficult or impossible to obtain in the past, and the preliminary observations allude to many exciting scientific findings to come.</p>

<p> The amplitude and spectral shape of shortwave radiation are used to retrieve aerosol and cloud properties from airborne and ground based measurements. By interacting with clouds and aerosols in the Earth's atmosphere, the wavelength-dependent radiation emitted by the sun is modified. This thesis presents the change in radiation due to absorption and scattering by clouds and aerosols, which result in distinct spectral signatures in shortwave radiation spectra. </p><p> The spectral signature in shortwave radiation due to aerosols is quantified by airborne measurements of irradiance above and below aerosol layers. This radiative effect is quantified by the relative forcing efficiency, which is used to compare the impact of aerosols from different air masses, locations, and time of day. The relative forcing efficiency is the net irradiance change due to the presence of aerosols normalized by aerosol optical thickness and incident irradiance. It is shown to vary by less than 20% per unit of midvisible aerosol optical thickness for aerosols sampled during 4 different experiments, except for highly absorbing aerosols near Mexico City. The similarity in relative forcing efficiency for these experiments, not expected a priori, suggests that this quantity is constrained for various types of aerosols with differing scattering and absorption characteristics even when surface albedo differs. To estimate the radiative effect of aerosols sampled in the Los Angeles basin during one of the experiments, where no concurrent measurements of optical thickness with spectral irradiance were available, a new iterative technique was devised to use aerosol optical thickness measurements from another airborne platform. </p><p> Cloud-transmitted zenith radiance spectra were measured from the ground in Boulder, Colorado. In these measurements, spectral signatures of cloud optical and microphysical properties were uncovered. The spectral signatures are the result of radiation that is transmitted through clouds, where ice or liquid water cloud particles modulate the radiation by absorbing and scattering incident light in a wavelength-dependent manner. Typically, the magnitudes of radiance at 2 wavelengths have been used to retrieve cloud properties, but by using wavelength-dependent features more sensitivity to cloud microphysical properties is obtained. This thesis presents a method to analyze wavelength-dependent signal, where spectral features such as slopes, curvatures, and shifts in locations of maxima and minima are parameterized. These spectral features found in normalized radiance are quantified by introducing 15 parameters. These 15 parameters form the basis of a new generalized retrieval obtaining cloud optical thickness (&tau;), effective radius (<i>r_e</i>), and thermodynamic phase (&phis;). When applied to a liquid water cloud case, this retrieval matched a measured transmittance spectrum with a smaller root mean square difference over the entire spectrum (3.1%) than two other methods (up to 6.4%). To quantify the retrieval over all possible combinations of &tau;, <i> r_e</i>, and &phis;, simulated measurements were used in conjunction with realistic measurement and model error characteristics. By combining these error characteristics within the GEneralized Nonlinear Retrieval Analysis (GENRA) a solution probability distributions can be built. The information of cloud properties contained within cloud-transmitted radiance is greater on average for liquid water clouds than for ice clouds. For all possible combinations of cloud properties, radiance transmitted through clouds with &tau;&lt;20 contain the most information on cloud properties, indicating that the 15 parameters have greatest sensitivity to cloud properties of optically thin clouds (&tau;&lt;20). Of the 15 parameters, only 10 are required to retrieve accurately &tau;, <i> r_e</i>, and &phis; for any cloud except for ice clouds with &tau;>25 and <i>r_e</i>>30 &mu;m. Using this retrieval, the correct thermodynamic phase is determined from transmittance with a probability greater than 99.4% for horizontally homogeneous clouds that contain either ice or liquid water cloud particles.</p>