Janet L. Machol

Preliminary measurements with an automated compact differential absorption lidar for the profiling of water vapor

The design and preliminary tests of an automated differential absorption lidar (DIAL) that profiles water vapor in the lower troposphere are presented. The instrument, named CODI (for compact DIAL), has been developed to be eye safe, low cost, weatherproof, and portable. The lidar design and its unattended operation are described. Nighttime intercomparisons with in situ sensors and a radiosonde are shown. Desired improvements to the lidar, including a more powerful laser, are also discussed.

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...

Evaluation of OVATION Prime as a forecast model for visible aurorae

This study evaluates the ability of the OVATION Prime auroral precipitation model to provide operational forecasts of the visible aurora. An operational implementation would primarily provide the general public with some guidance for viewing the aurora. We evaluate the likelihood that if aurorae are predicted to be visible at a location, they will be seen there within the hour. Nighttime model forecasts were validated with Polar Ultraviolet Imager data for Kp ≥ 3 and for the years 1997 and 1998. The overall forecasts for a visible aurora to occur or to not occur were correct 77% of the time. The most important prediction for public auroral viewing is that the visible aurora will occur, and these forecasts were correct 86% of the time.

Optical studies of IV–VI quantum dots

PbS microcrystallites show strong quantum confinement effects on account of the fact that the particle size is much smaller than the exciton Bohr radius, leading to large blue shifts of the optical absorption edge and the transverse optical phonon frequencies. In addition, femtosecond pump-probe experiments find a transient absorption with tetrahertz oscillatory behavior, due to vibrational quantum beats. The frequency of the tetrahertz response agrees with the fundamental infrared absorption of the PbS microcrystallites, suggesting that the vibrational mode to which the photoexcited carriers couple is a transverse optical phonon.

Comparison of the pseudorandom noise code and pulsed direct-detection lidars for atmospheric probing

The advantages and limitations of using the pseudorandom-noise (PN)-code technique in comparison with pulsed direct detection are discussed. Because the signal-to-noise ratio (SNR) of the PN codes is dependent on the average atmospheric return, strong returns from short ranges and clouds determine the SNR for all ranges. The SNR of a profile obtained by pulsed direct detection exceeds that of the PN-code technique for laser beams with the same average power.

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.

New Solar Irradiance Measurements from the Miniature X-Ray Solar Spectrometer Cubesat

The goal of the Miniature X-ray Solar Spectrometer (MinXSS) CubeSat is to explore the energy distribution of soft X-ray (SXR) emissions from the quiescent Sun, active regions, and during solar flares, and to model the impact on Earths ionosphere and thermosphere. The energy emitted in the SXR range (0.1 --10 keV) can vary by more than a factor of 100, yet we have limited spectral measurements in the SXRs to accurately quantify the spectral dependence of this variability. The MinXSS primary science instrument is an Amptek, Inc. X123 X-ray spectrometer that has an energy range of 0.5--30 keV with a nominal 0.15 keV energy resolution. Two flight models have been built. The first, MinXSS-1, has been making science observations since 2016 June 9, and has observed numerous flares, including more than 40 C-class and 7 M-class flares. These SXR spectral measurements have advantages over broadband SXR observations, such as providing the capability to derive multiple-temperature components and elemental abundances of coronal plasma, improved irradiance accuracy, and higher resolution spectral irradiance as input to planetary ionosphere simulations. MinXSS spectra obtained during the M5.0 flare on 2016 July 23 highlight these advantages, and indicate how the elemental abundance appears to change from primarily coronal to more photospheric during the flare. MinXSS-1 observations are compared to the Geostationary Operational Environmental Satellite (GOES) X-Ray Sensor (XRS) measurements of SXR irradiance and estimated corona temperature. Additionally, a suggested improvement to the calibration of the GOES XRS data is presented.

Proposed Compact, Eye-Safe Lidar for Measuring Atmospheric Water Vapor

A thorough understanding of tropospheric water vapor is essential for forecasting weather and modeling radiative transfer. This project focuses on the development of an automated, ground-based, compact, eye-safe and inexpensive differential absorption lidar (DIAL) to profile tropospheric water vapor. Such a system could be widely deployed to supplement twice-daily radiosonde profiles or used in arrays to measure water vapor transport variability with a continuous datastream from a known location. Instrument features will include daytime measurement capabilities, a detection range of 3–6 km, a spatial resolution of 100 m, a temporal resolution of ~15 minutes, and an error of less than 1 g/kg. This paper discusses the results of a lidar simulation and solid-state laser options for use in a low-cost water vapor lidar.

Remote sensing of the nocturnal boundary layer for wind energy applications.

The fine temporal and spatial resolution of Doppler lidar observations has been highly effective in the study of wind and turbulence dynamic in the nocturnal boundary layer during Lamar Low-Level Project in 2003. The High-Resolution Doppler Lidar (HRDL), designed and developed at the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL), measures range-resolved profiles of line-of sight (LOS) Doppler velocity and aerosol backscatter with a pulse repetition frequency of 200 Hz, velocity precision about 10 cm s-1, and a very narrow beam width. The majority of the lidar-measured wind speed and variance profiles were derived using a vertical-scan mode and the application of a vertical binning technique. The profile data were used to calculate quantities important for wind energy applications, including turbulence intensity, wind and directional shear through the layer of the turbine rotor. Profiles of all quantities show a strong variation with height. The mean wind fields, the turbulence, and turbulence intensities show a good agreement with sonic anemometer sodar high confidence (high SNR) measurements. The ability of HRDL to provide continuous information about wind and turbulence conditions at the turbine height and above the range of the tower measurements made HRDL as a powerful instrument for studies of the nighttime boundary layer features. Such information is needed as turbine rotors continue to rise higher into the boundary layer.

Tunable ultraviolet femtosecond pulses at kilohertz repetition rates

Femtosecond pulses, tunable between 250 and 400 nm, are generated at a pulse repetition rate of 8 kHz by two methods, sum-frequency generation and second-harmonic generation. Both methods produce pulse energies ranging from ~ 10 pJ at 280 and 380 nm to 40 nJ at 310 nm. Between 250 and 280 nm, sum-frequency generation produces pulses with energies significantly greater than those produced by second-harmonic generation. The measured pulse duration at 310 nm is 180 fs.