Timothy A. Cook

Measurement of ozone and water vapor by Airbus in-service aircraft: The MOZAIC airborne program, an overview

Tentative estimates, using three-dimensional chemistry and transport models, have suggested small ozone increases in the upper troposphere resulting from current aircraft emissions, but have also concluded to significant deficiencies in todays models and to the need to improve them through comparison with extended data sets. The Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program was initiated in 1993 by European scientists, aircraft manufacturers, and airlines to collect experimental data. Its goal is to help understand the atmosphere and how it is changing under the influence of human activity, with particular interest in the effects of aircraft. MOZAIC consists of automatic and regular measurements of ozone and water vapor by five long range passenger airliners flying all over the world. The aim is not to detect direct effects of aircraft emissions on the ozone budget inside the air traffic corridors but to build a large database of measurements to allow studies of chemical and physical processes in the atmosphere, and hence to validate global chemistry transport models. MOZAIC data provide, in particular, detailed ozone and water vapor climatologies at 9–12 km where subsonic aircraft emit most of their exhaust and which is a very critical domain (e.g., radiatively and stratosphere/troposphere exchanges) still imperfectly described in existing models. This will be valuable to improve knowledge about the processes occuring in the upper troposphere and the lowermost stratosphere, and the model treatment of near tropopause chemistry and transport. During MOZAIC I (January 1993–September 1996), fully automatic devices were developed, installed aboard five commercial Airbus A340s, and flown in normal airline service. A second phase, MOZAIC II, started in October 1996 with the aim of continuing the O3 and H2O measurements and doing a feasibility study of new airborne devices (CO, NOy). Between September 1994 and December 1997, 7500 flights, representing 54,000 flight hours, were made over the continents (Europe, North America, Asia, South America, and Africa) and the Atlantic Ocean. Most of the measurements (90%) correspond to cruise altitudes (9–12 km), the remaining being obtained during ascents and descents near the 50 cities frequented by MOZAIC operations. This paper reports the main characteristics of the program and the flights, with a brief summary of the general content and focus of papers already published and companion papers of this special issue. These deal with the following: description and validation of the ozone and water vapor measurement methods; presentation of an accurate ozone climatology at 9–12 km altitude, over the Northern Hemisphere (130°W–140°E; 0°–80°N), and down to 30°S over South America and Africa; comparison between a 2-year MOZAIC ozone climatology (1994–1996; 0–12 km) and a long series of older measurements made since the 1980s at 8 stations of the Ozone Sounding Network; study of ozone-rich transients, up to 500 ppbv on a horizontal scale of 5–80 km, in the upper tropical troposphere; and comparison between MOZAIC ozone data and output from the global chemistry and transport model (CTM) TOMCAT.

Two-dimensional mapping of the plasma density in the upper atmosphere with computerized ionospheric tomography (CIT)

Tomographic imaging of the ionosphere is a recently developed technique that uses integrated measurements and computer reconstructions to determine electron densities. The integral of electron density along vertical or oblique paths is obtained with radio transmissions from low-earth-orbiting (LEO) satellite transmitters to a chain of receivers on the earth’s surface. Similar measurements along horizontal paths can be made using transmissions from Global Position System (GPS) navigation satellites to GPS receivers on LEO spacecraft. Also, the intensities of extreme ultraviolet (EUV) emissions can be measured with orbiting spectrometers. These intensities are directly related to the integral of the oxygen ion and electron densities along the instrument line of sight. Two-dimensional maps of the ionospheric plasma are produced by analyzing the combined radio and EUV data using computerized ionospheric tomography (CIT). Difficulties associated with CIT arise from the nonuniqueness of the reconstructions, owi...

A statistical framework for space‐based EUV ionospheric tomography

We present a statistical reconstruction framework for space-based extreme ultraviolet (EUV) ionospheric tomography. The EUV technique offers a means to invert the nighttime F region electron density on global scales from a single spaceborne spectrograph, using prominent optically thin emissions produced by radiative recombination of O+. Since the EUV technique does not rely on ground receivers to make the measurements, the observations do not suffer from limitations on the viewing angles. The EUV tomography is an ill-conditioned inverse problem in the sense that its solution is sensitive to perturbations of the measured data. With large condition numbers of a typical projection matrix, simple least squares inversion techniques yield unacceptable results in the presence of noise. This reflects the fact that more degrees of freedom are being sought than are supported by the noisy data. To overcome this limitation, we cast the tomographic inverse problem in a stochastic framework and incorporate a statistical prior model. In doing so we also obtain measures of estimation uncertainty for the solutions. Through simulations, we demonstrate the applicability of these techniques in the context of a space mission designed for EUV ionospheric tomography, namely, the Tomographic Experiment Using Radiative Recombinative Ionospheric EUV and Radio Sources (TERRIERS). The simulations show promising results for EUV tomography as a viable ionospheric remote sensing technique.

Finding Leaves in the Forest: The Dual-Wavelength Echidna Lidar

The dual-wavelength Echidna lidar is a portable ground-based full-waveform terrestrial scanning lidar for characterization of fine-scale forest structure and biomass content. While scanning, the instrument records the full time series of returns at a half-nanosecond rate from two coaligned 5-ns pulsed lasers at 1064 and 1548 nm wavelengths. Leaves absorb more strongly at 1548 nm compared to stems, allowing discrimination of forest composition at milliradian scales from the ground to the forest canopy. This work describes the instrument design and data products and demonstrates the power of two wavelength lidar to clearly distinguish leaves from woody material with preliminary field data from the Sierra Nevada National Forest.

DWEL: A Dual-Wavelength Echidna Lidar for ground-based forest scanning

The Dual-Wavelength Echidna® Lidar (DWEL), a ground-based, full-waveform lidar scanner designed for automated retrieval of forest structure, uses simultaneously-pulsing, 1064 nm and 1548 nm lasers to separate scattering by leaves from scattering by trunks, branches, and ground materials. Leaf hits are separated from others by a reduced response at 1548 nm due to water absorption by leaf cellular contents. By digitizing the full return-pulse waveform (full-width half maximum, 1.5 m) at 7.5 cm intervals, the scanner can identify the type of scattering event, as well as identify and separate multiple scattering events along the pulse path to reconstruct multiple hits at distances of up to 100 m from the scanner. Scanning covers zenith angles of 0-119° and 360 azimuth with pulse centers spaced at 4, 2, and 1 mrad intervals, providing spatial resolutions of 4-40, 2-20, and 1-10 cm respectively at 10 and 100 m distances. The instrument is currently undergoing integration and testing for field deployment in July-August, 2012.

Daytime wave characteristics in the mesosphere lower thermosphere region: Results from the Balloon‐borne Investigations of Regional‐atmospheric Dynamics experiment

Results obtained from a joint INDO-US experiment on the investigations of mesosphere/lower thermosphere wave dynamics using balloon-borne optical dayglow measurements in combination with ground-based optical, radio, and magnetometer data are presented. Ultraviolet OI 297.2 nm dayglow emissions that originate at ~ 120 km were measured from low-magnetic latitudes from onboard a balloon on 8 March 2010. This paper describes the details of a new spectrograph that is capable of making high spectral resolution (0.2 nm at 297.2 nm) and large (80°) field of view ultraviolet dayglow emission measurements and presents the first results obtained from its operation onboard a high-altitude balloon. Waves of scale sizes ranging from 40 to 80 km in the zonal direction were observed in OI 297.2 nm emissions. Meridional scale sizes of similar waves were found to be 200 km as observed in the OI 557.7 nm emissions that originate from ~ 100 km. Periodicities were also derived from the variations of equatorial electrojet strength and ionospheric height on that day. Common periodicities of waves (in optical, magnetic, and radio measurements) were in the range of 16 to 30 min, which result in intrinsic horizontal wave speeds in the range of 21 to 77 m s−1. It is argued that gravity waves of such scale sizes and speeds at these heights are capable of propagating well into the thermosphere because the background wind directions were favorable. These waves were potentially capable of forming the seeds for the generation of equatorial plasma irregularities which did occur on that night.

PICTURE: a sounding rocket experiment for direct imaging of an extrasolar planetary environment

The Planetary Imaging Concept Testbed Using a Rocket Experiment (PICTURE 36.225 UG) was designed to directly image the exozodiacal dust disk of ǫ Eridani (K2V, 3.22 pc) down to an inner radius of 1.5 AU. PICTURE carried four key enabling technologies on board a NASA sounding rocket at 4:25 MDT on October 8th, 2011: a 0.5 m light-weight primary mirror (4.5 kg), a visible nulling coronagraph (VNC) (600-750 nm), a 32x32 element MEMS deformable mirror and a milliarcsecond-class fine pointing system. Unfortunately, due to a telemetry failure, the PICTURE mission did not achieve scientific success. Nonetheless, this flight validated the flight-worthiness of the lightweight primary and the VNC. The fine pointing system, a key requirement for future planet-imaging missions, demonstrated 5.1 mas RMS in-flight pointing stability. We describe the experiment, its subsystems and flight results. We outline the challenges we faced in developing this complex payload and our technical approaches.

Interplanetary H Lyα Observations from a Sounding Rocket

We describe a Self-Compensating All-Reflecting Interferometer used to measure diffuse interplanetary H Ly? emission (? ~ 1216 ?) of interstellar origin at high spectral resolution (?/?? ~ 100,000). The instrument is capable of resolving the separation between the Doppler-shifted, interplanetary neutral H emission from the Earths geocoronal emission line. We present the optical layout and mechanical design that enable the instrument to maintain alignment through a sounding rocket flight. We find an H Ly? spectrum, including both geocoronal emission and interplanetary scattered features, which we have fitted using Gaussian line profiles. The interplanetary H line is fitted with a 7900 ? 2400 K line width. The geocoronal line width is fitted with a 1900 ? 500 K Gaussian. The Doppler shift between the geocoronal and interplanetary line is 0.145 ?, corresponding to an apparent interplanetary wind velocity of 16 ? 7 km s-1. We show how full line-profile measurements of interplanetary H emission can advance current studies of the heliospheric interface region and very local interstellar medium.

Single-element imaging spectrograph

A spectrograph concept designed for both high wavelength and high spatial resolution (in one dimension) is briefly described. This design is referred to as a single-element imaging spectrograph (SEIS). It is a one-bounce diffractive system that combines the spectral properties of a Rowland mount spectrograph with the imaging (spatial resolution) properties of a Wadsworth mount spectrograph through the use of a toroidal diffraction grating. No primary optics are necessary, making the system especially attractive for use in the extreme and far ultraviolet, where low reflectivity of common optical coatings can severely limit instrument sensitivity.

Helium and argon abundance constraints and the thermal evolution of Comet Austin (1989c1)

Abstract We report results from the flight of a rocket-borne, far ultraviolet (FUV) spectrometer observation to establish upper limits on He and Ar abundances in the bright, dynamically “new,” comet Austin (1989c1). Previous to comet Austing, no comet had been spectroscopically observed to set helium and argon abundance constraints. Relative to solar abundance, our upper limits imply Comet Austin is at least 1.5 × 10 4 depleted in He/O, and no more than 30 times enriched in Ar/O. These upper limits allow us to discuss the thermal conditions experienced by this comet during its formation and during its subsequent evolution. The upper limits achieved by this 258-sec subortial rocket observation indicate the usefulness of future, longer-integrated or otherwise more sensitive observations of comets below 1200 A, in the FUV.