Matthew James McGill

Visible wavelength Doppler lidar for measurement of wind and aerosol profiles during day and night

An incoherent (direct detection) Doppler lidar is developed that operates in the middle of the visible spectrum and measures wind and aerosol profiles during the day and night from the planetary boundary layer to the lower stratosphere. The primary challenge of making a lidar measurement in the visible spectrum during daylight hours is the strong presence of background light from the sun. To make a measurement of this type, the laser line must be isolated spectrally to the greatest extent possible. This has been accomplished through the use of a multiple etalon Fabry-Perot interferometer in combination with a narrow-band filter. The incoherent technique and system are a modified version of the Fabry-Perot interlerometer and image-plane detector technology developed for an earlier Doppler lidar developed at the University of Michigan and for the High-Resolution Doppler Imager (HRDI) now flying on the Upper Atmosphere Research Satellite. The incoherent Doppler analysis is discussed and sample measurements are shown. Winds are measured in the boundary layer with 100-m vertical resolution and 5-mm temporal resolution with 1 to 3 m s-1 accuracy.

The Multiple Altimeter Beam Experimental Lidar (MABEL): An Airborne Simulator for the ICESat-2 Mission

AbstractThis paper presents the motivation for, and initial results from, the Multiple Altimeter Beam Experimental lidar (MABEL) instrument. The MABEL instrument provides a new capability for airborne altimetry measurements and serves as a prototype and simulator for the upcoming NASA second-generation Ice, Cloud, and Land Elevation Satellite (ICESat-2) mission. Designed to be highly flexible in measurement capability, MABEL serves as both a demonstration of measurement capability and a science tool for cryospheric and biospheric remote sensing. It is important to document the instrument specifications and essential background information to provide a suitable reference for the detailed MABEL results and science investigation publications that will be forthcoming.

Statistics of Cloud Optical Properties from Airborne Lidar Measurements

AbstractAccurate knowledge of cloud optical properties, such as extinction-to-backscatter ratio and depolarization ratio, can have a significant impact on the quality of cloud extinction retrievals from lidar systems because parameterizations of these variables are often used in nonideal conditions to determine cloud phase and optical depth. Statistics and trends of these optical parameters are analyzed for 4 yr (2003–07) of cloud physics lidar data during five projects that occurred in varying geographic locations and meteorological seasons. Extinction-to-backscatter ratios (also called lidar ratios) are derived at 532 nm by calculating the transmission loss through the cloud layer and then applying it to the attenuated backscatter profile in the layer, while volume depolarization ratios are computed using the ratio of the parallel and perpendicular polarized 1064-nm channels. The majority of the cloud layers yields a lidar ratio between 10 and 40 sr, with the lidar ratio frequency distribution centered ...

Multiple Fabry-Pe´rot interferometers in an incoherent Doppler lidar

A high-resolution incoherent-detection Doppler lidar has been constructed at the University of Michigan Space Physics Research Laboratory. The lidar uses multiple Fabry-Pe´ rot interferometers to measure the Doppler shift of aerosol-backscattered light and to attenuate background light. In this way, vertical profiles of the horizontal wind field are obtained with high spatial and temporal resolution. It has been found that if the transmission functions of the etalons are not properly aligned, a systematic error in the Doppler-shift determination can result. This error is dependent on the relative aerosol loading of the atmosphere and can be quite large. For large etalon offsets the wind error can be in excess of 10 m/s. Even for small offsets and high aerosol loadings, the wind determination can be biased by as much as 1 m/s. A previously developed model and inversion process can be modified to allow for an offset between the etalons and recover data without bias.

Holographic circle-to-point converter with particular applications for lidar work

A holographic optical element is developed that functions as a circle-to-point converter. The holographic plate looks like a zone plate but functions like a collection of field lenses. Each annulus of the holo- graphic plate acts as a separate lens, imaging incident light to a point focus. The plate was developed for use with Fabry-Perot interferom- eters, but other applications are also possible. The plate has high throughput, and when coupled with high quantum efficiency solid state detectors provides an efficient photon-collecting detection system. De- velopment of the plate was driven by need for an efficient Doppler lidar detection system, and specific lidar applications are discussed.

The Airborne Cloud-Aerosol Transport System: Overview and Description of the Instrument and Retrieval Algorithms

AbstractThe Airborne Cloud–Aerosol Transport System (ACATS) is a Doppler wind lidar system that has recently been developed for atmospheric science capabilities at the NASA Goddard Space Flight Center (GSFC). ACATS is also a high-spectral-resolution lidar (HSRL), uniquely capable of directly resolving backscatter and extinction properties of a particle from a high-altitude aircraft. Thus, ACATS simultaneously measures optical properties and motion of cloud and aerosol layers. ACATS has flown on the NASA ER-2 during test flights over California in June 2012 and science flights during the Wallops Airborne Vegetation Experiment (WAVE) in September 2012. This paper provides an overview of the ACATS method and instrument design, describes the ACATS HSRL retrieval algorithms for cloud and aerosol properties, and demonstrates the data products that will be derived from the ACATS data using initial results from the WAVE project. The HSRL retrieval algorithms developed for ACATS have direct application to future s...

Measurement of aerosol loading profiles and mixing heights in Atlanta, Georgia during the 1992 SORP-ONA field study

The Southern Oxidants Research Program on Ozone Non-Attainment (SORP-ONA) field study was held in Atlanta, Georgia, during the summer of 1992. SORP-ONA was the first in a series of intensive studies to characterize urban ozone in the South as a part of the Southern Oxidants Study (SOS). The University of Michigan Doppler Lidar was stationed on the Georgia Tech Campus during the study and measured aerosol profiles with approximately 15-minute temporal resolution. A study of mixing in the urban boundary layer determined that aerosol and presumably chemical constituents are not always well-mixed as expected and that some structure does exist. A technique for separation of aerosol and molecular scattered signal for retrieval of aerosol profiles is described. Additionally, a technique is introduced to estimate boundary layer mixing height which shows excellent correlation with rawinsonde potential temperature profile estimates of mixing height.

Incoherent Doppler LIDAR for continuous measurement of wind and aerosol profiles

The University of Michigan Space Research Laboratory has developed a mobile, high spectral resolution incoherent Doppler lidar capable of measuring wind and aerosol loading profiles in the troposphere and lower stratosphere. The system uses a 3 Watt pulsed frequency doubled Nd:YAG laser operating at 532 nm. The backscattered signal is collected by a 44.4 cm diameter Newtonian telescope. A two axis mirror scanning system allows the instrument to achieve full sky coverage. Active feedback control of key instrument elements provides an overall instrument stability of better than 1 m/s. A pair of Fabry-Perot interferometers in combination with a narrowband (0.05 nm) interference filter are used to filter daylight background and provide a high spectral resolving element to measure the Doppler shift. In addition, the aerosol and molecular scattered components of the signal can be separated, giving a measure of the relative aerosol loading. Measurements have been made day and night in the boundary layer with vertical resolution of 100 meters and a temporal resolution of approximately 6 minutes. Accuracy of the wind velocity is on the order of 1-2 m/s in the boundary layer. Continuous measurements on this temporal scale should prove highly useful in parameterizing atmospheric aerosol movement, cloud evolution, and wind field variability.<<ETX>>

Visible wavelength Doppler Lidar for measurement of wind and aerosol profiles during day and night

The University of Michigans Space Physics Research Laboratory has constructed a mobile high-spectral-resolution Doppler lidar capable of measuring wind and aerosol loading profiles in the troposphere and lower stratosphere. The system uses a 3-W pulsed frequency-doubled Nd:YAG laser operating at 532 nm as the active source. Backscattered signal is collected by a 44.4-cm-diameter Newtonian telescope. A two axis mirror scanning system allows the instrument to achieve full sky coverage. A pair of Fabry-Perot interferometers in combination with a narrowband (0.1nm) interference filter are used to filter daylight background and provide a high spectral resolving element to measure the Doppler shift. In addition, the aerosol and molecular scattered components of the signal can be separated, giving a measure of the relative aerosol loading. Measurements have been made day and night in the boundary layer with vertical resolution of 100 m and a temporal resolution of approximately 5 minutes. Accuracy of the wind velocity is on the order of 1 to 2 m/s in the boundary layer.

Development of an Autonomous Lidar Instrument for Use on a UAV Platform [invited]

Researchers at NASAs Goddard Space Flight Center have developed an autonomous aerosol backscatter lidar instrument for use on the high-altitude ER-2 research aircraft. This instrument, known as the Cloud Physics Lidar (CPL), has proven highly valuable to NASA over the past five years. The CPL has been used extensively for studies of clouds, dust, and aerosols and for satellite validation activities. Because the future of NASAs suborbital program appears to rely heavily on Unmanned Aerial Vehicles (UAVs), and because CPL have been essential for NASA science and satellite validation, it is highly desirable to have a similar measurement capability available for use on UAVs. To meet this need, work is currently underway to transfer this instrument to a UAV platform. Our approach is to build a duplicate of the proven successful CPL instrument, which can be done with low cost and low risk. While the NASA applications are Earth science and satellite validation, there are also Homeland Security and non-NASA science applications for such an instrument.