Richard D. Marchbanks

Development and Application of a Compact, Tunable, Solid-State Airborne Ozone Lidar System for Boundary Layer Profiling

AbstractThe National Oceanic and Atmospheric Administration/Earth System Research Laboratory/Chemical Sciences Division (NOAA/ESRL/CSD) has developed a versatile, airborne lidar system for measuring ozone and aerosols in the boundary layer and lower free troposphere. The Tunable Optical Profiler for Aerosol and Ozone (TOPAZ) lidar was deployed aboard a NOAA Twin Otter aircraft during the Texas Air Quality Study (TexAQS 2006) and the California Research at the Nexus of Air Quality and Climate Change (CalNex 2010) field campaigns. TOPAZ is capable of measuring ozone concentrations in the lower troposphere with uncertainties of several parts per billion by volume at 90-m vertical and 600-m horizontal resolution from an aircraft flying at 60 m s−1. The system also provides uncalibrated aerosol backscatter profiles at 18-m vertical and 600-m horizontal resolution. TOPAZ incorporates state-of-the-art technologies, including a cerium-doped lithium calcium aluminum fluoride (Ce:LiCAF) laser, to make it compact an...

Oceanographic lidar profiles compared with estimates from in situ optical measurements

Oceanographic lidar profiles measured in an aerial survey were compared with in situ measurements of water optical properties made from a surface vessel. Experimental data were collected over a two-week period in May 2010 in East Sound, Washington. Measured absorption and backscatter coefficients were used with the volume-scattering function in a quasi-single-scattering model to simulate an idealized lidar return, and this was convolved with the measured instrument response to accurately reproduce the measured temporal behavior. Linear depth-dependent depolarization from the water column and localized depolarization from scattering layers are varied to fine tune the simulated lidar return. Sixty in situ measurements of optical properties were correlated with nearly collocated and coincident lidar profiles; our model yielded good matches (±3 dB to a depth of 12 m) between simulated and measured lidar profiles for both uniform and stratified waters. Measured attenuation was slightly higher (5%) than diffuse attenuation for the copolarized channel and slightly lower (8%) for the cross-polarized channel.

Scanning tropospheric ozone and aerosol lidar with double-gated photomultipliers

The Ozone Profiling Atmospheric Lidar is a scanning four-wavelength ultraviolet differential absorption lidar that measures tropospheric ozone and aerosols. Derived profiles from the lidar data include ozone concentration, aerosol extinction, and calibrated aerosol backscatter. Aerosol calibrations assume a clear air region aloft. Other products include cloud base heights, aerosol layer heights, and scans of particulate plumes from aircraft. The aerosol data range from 280 m to 12 km with 5 m range resolution, while the ozone data ranges from 280 m to about 1.2 km with 100 m resolution. In horizontally homogeneous atmospheres, data from multiple-elevation angles is combined to reduce the minimum altitude of the aerosol and ozone profiles to about 20 m. The lidar design, the characterization of the photomultiplier tubes, ozone and aerosol analysis techniques, and sample data are described. Also discussed is a double-gating technique to shorten the gated turn-on time of the photomultiplier tubes, and thereby reduce the detection of background light and the outgoing laser pulse.

ETL's transportable lower-troposphere ozone lidar and its applications in air-quality studies

A transportable ground-based differential absorption lidar specifically designed for ozone and aerosol profiling in the lower troposphere was developed at the National Oceanic and Atmospheric Administration/Environmental Technology Laboratory (NOAA/ETL). The NOAA/ETL ozone lidar has the unique capability of measuring vertical profiles of ozone concentration from near the surface up to 3 km, and measuring vertical profiles of aerosol from the surface to about 10 km. The innovative hardware design and improved signal processing techniques make the system efficient, compact, and easily transportable. A recently implemented 2D scanning system provides the capability of measuring ozone concentrations and aerosol in a vertical plane. The lidar has been deployed in seven field experiments in California, Illinois, and Boulder, Colorado since summer 1993. Lidar observations of vertical profiles of ozone concentrations and ozone advection fluxes in Southern California during high ozone season revealed interesting structures of ozone distributions in the Los Angeles urban area, and near the Cajon Pass which is a major corridor of ozone transport from Los Angeles to the Mojave Desert.

Optical Backscattering Measured by Airborne Lidar and Underwater Glider

The optical backscattering from particles in the ocean is an important quantity that has been measured by remote sensing techniques and in situ instruments. In this paper, we compare estimates of this quantity from airborne lidar with those from an in situ instrument on an underwater glider. Both of these technologies allow much denser sampling of backscatter profiles than traditional ship surveys. We found a moderate correlation (R = 0.28, p < 10−5), with differences that are partially explained by spatial and temporal sampling mismatches, variability in particle composition, and lidar retrieval errors. The data suggest that there are two different regimes with different scattering properties. For backscattering coefficients below about 0.001 m−1, the lidar values were generally greater than the glider values. For larger values, the lidar was generally lower than the glider. Overall, the results are promising and suggest that airborne lidar and gliders provide comparable and complementary information on optical particulate backscattering.

Inversion of oceanographic profiling lidars by a perturbation to a linear regression

We present a simple, robust inversion for airborne oceanographic lidar profiles. A linear regression to the logarithm of the return is followed by a perturbation to obtain a backscatter estimate. For typical thin plankton layer examples, errors are expected to be <10% over 90% of the ocean. The inversion was applied to lidar data off the coast of Florida, where the correlation between lidar backscatter at 5xa0m and surface chlorophyll concentration from satellite ocean color measurements was 0.92.

Optical remote sensing of sound in the ocean

We are proposing a novel remote sensing technique to measure sound in the upper ocean. The objective is a system that can be flown on an aircraft. Conventional acoustic sensors are ineffective in this application, because almost none (~ 0.1 %) of the sound in the ocean is transmitted through the water/air interface. The technique is based on the acoustic modulation of bubbles near the sea surface. It is clear from the ideal gas law that the volume of a bubble will decrease if the pressure is increased, as long as the number of gas molecules and temperature remain constant. The pressure variations associated with the acoustic field will therefore induce proportional volume fluctuations of the insonified bubbles. The lidar return from a collection of bubbles has been shown to be proportional to the total void fraction, independent of the bubble size distribution. This implies that the lidar return from a collection of insonified bubbles will be modulated at the acoustic frequencies, independent of the bubble size distribution. Moreover, that modulation is linearly related to the sound pressure. The basic principles have been demonstrated in the laboratory, and these results will be presented. Estimates of signal-to-noise ratio suggest that the technique should work in the open ocean. Design considerations and signal-to-noise ratios will also be presented.

Airborne lidar sensing of internal waves in a shallow fjord

A dual polarization lidar was used to sense internal waves from a small aircraft. Internal waves are gravity waves that are formed by a vertical displacement of a density gradient in the ocean. If the perturbation is great enough, a nonlinear wave is produced and the balance between nonlinearity and dispersion can create a soliton-like wave packet. We observed nonlinear wave packets in West Sound, Orcas Island, Washington. In this region, a density gradient is formed in the summer by solar heating of the surface water. The perturbation is produced by strong tidal flow through a narrow, shallow channel at the mouth of the sound. Plankton layers form in association with the density gradients, and these layers produce an enhanced lidar return that moves up and down with the wave. We observed these internal waves with a lidar operating at 532 nm. They were much more visible when the receiver was polarized orthogonal to the transmitted laser pulse. This was the case whether linear or circular polarization was used, with no significant difference between the two cases. These internal waves were also visible to the naked eye, when the surface currents produced by the waves modulated the small surface waves that produce the apparent texture of the ocean surface.

Lidar as a tool for fisheries management

This paper describes the results of a series of airborne observations of sardine schools off the coast of California in the fall of 2010. The lidar system used a linearly-polarized transmitter and a single receiver that was sensitive to the backscattered light in the orthogonal polarization. The aircraft was also equipped with a camera to photograph schools. The camera had a broader swath than the lidar, so was able to see more of the schools at the surface. However, the lidar detected schools much deeper in the water, was not hampered by waves and sun glare, and could survey at night. The combination of lidar and photographs proved to be a very powerful survey tool for sardines, since the latter was able to identify surface targets that appear very similar to fish schools in the lidar return. Examples of these include floating mats of kelp and ship wakes.