Michael E. Dobbs

The high-resolution Doppler imager on the Upper Atmosphere Research Satellite

The high-resolution Doppler imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) is a triple-etalon Fabry-Perot interferometer designed to measure winds in the stratosphere, mesosphere, and lower thermosphere. Winds are determined by measuring the Doppler shifts of rotational lines of the O2 atmospheric band, which are observed in emission in the mesosphere and lower thermosphere and in absorption in the stratosphere. The interferometer has high resolution (0.05 cm−1), good offband rejection and excellent stability. This paper provides details of the design and capabilities of the HRDI instrument.

High-speed CW lidar retrieval using spectral lock-in algorithm

A continuous-wave (CW) NIR carbon-dioxide monitoring system, incorporating Wavelength Modulation Spectroscopy (WMS), has been developed and was tested aboard the Spirit of Goodyear airship platform. The data shows sensitivities nearly identical to previous ground-based tests but with much higher information rates (100Hz). These tests were conducted over regions with varying ground albedo and included path lengths up to 1.5 km. The system utilized commercial-off-the-shelf (COTS) components including telecom laser diodes and amplifiers. Currently, the system is limited by Erbium Doped Fiber Amplifier (EDFA) spectral bandwdith, but the ever-increasing average power of quantum cascade lasers coupled with the development of midwave fiber technology could make this CW-based architecture a viable solution for future airborne sensors in the MWIR region.

Validation of design for space-based tunable diode laser absorption spectroscopy payload

Significant progress has been made in the performance, qualification and validation of Active Remote Sensing systems to address complex questions in climate science from satellites in low earth orbit. During the past year, ITT has completed the design, qualified the components, and validated the performance of sophisticated Tunable Diode Laser Absorption Spectroscopy systems for airborne and space missions. ITT has shown that measurement of total column CO2 to an accuracy of 0.5% can be readily achieved using a 5 watt laser, 1 meter telescope and digital signal processing techniques to reject sunlight and noise. Furthermore, the design exploits the proven high reliability of photonic components developed by the telecom industry. ITT testing validated that these components survive launch and multi-year operation in space without significant degradation. Using a scaled sensor, the ground based validation campaign demonstrated the ability to accurately retrieve the CO2 diurnal cycle as well the automotive induced variations in CO2 observed in urban settings. These data validate the end-end sensor performance model and retrieval algorithms, which have previously been used to design a space based CO2 sensor proposed to NASA. ITT will discuss the application of these technologies to other atmospheric constituents. Combined, these results serve to demonstrate that laser based remote sensing of key components of the atmosphere which address global climate change can be achieved from low earth orbit without further development.

CO2 monitoring with a field-deployable NIR standoff environmental sensor

We report standoff open path atmospheric CO2 monitoring with a field deployable, turn key system including a continuous wave (CW)distributed feedback (DFB) laser and an erbium doped fiber amplifier (EDFA) at 1.5-μm. A sensitivity of 28-ppm was achieved over 1.5-km of open air with 200-pW of received power, a 10s acquisition time, and a peak absorption cross section of 8x10-23. This sensitivity corresponds to an error in fractional absorbance of 8x10-3. Closed cell lab sensitivities are better than 3000ppm*m, an error in fractional absorbance of 5x10-4. These results have been achieved using space qualified laser components, un-cooled InGaAs detectors, off the shelf electronics in a rugged all fiber architecture.

Determining the electron energy distribution near the plasma potential in the earth’s ionosphere

A determination of the plasma potential using an electrostatic analyzer is described in which the potential difference between the instrument slit system and surrounding plasma is minimized. Data obtained from rocket‐borne instrumentation demonstrate the viability of this technique for electron fluxes between thermal energies (∼0.5 V) and suprathermal energies (many volts).

Satellite-based measurements of CO 2 for carbon flux estimation

Satellite observations of atmospheric CO2 are the key to answering important questions regarding spatial and temporal variabilities of carbon sources and sinks. Global measurements sampling the air above land and oceans allow oceanic flux to be distinguished from terrestrial flux. Continuous sampling on frequent basis allows seasonal variations to be distinguished. This study quantifies the potential value of satellite-based measurements of column- integrated CO2 concentrations in terms of the carbon source/sink information that can be derived from these concentrations via inverse modeling. We discuss the utility of the carbon flux inversions in terms of both spatial and temporal resolution, compare capabilities of active and passive approaches to the measurements, and demonstrate the feasibility of high precision CO2 column concentration retrievals.

Satellite-based measurements of CO2 for carbon flux estimation

Satellite observations of atmospheric CO2 are the key to answering important questions regarding spatial and temporal variabilities of carbon sources and sinks. Global measurements sampling the air above land and oceans allow oceanic flux to be distinguished from terrestrial flux. Continuous sampling on frequent basis allows seasonal variations to be distinguished. This study quantifies the potential value of satellite-based measurements of column- integrated CO2 concentrations in terms of the carbon source/sink information that can be derived from these concentrations via inverse modeling. We discuss the utility of the carbon flux inversions in terms of both spatial and temporal resolution, compare capabilities of active and passive approaches to the measurements, and demonstrate the feasibility of high precision CO2 column concentration retrievals.

Optimization of space borne imaging ladar sensor for asteroid studies using parameter design

Imaging LADAR is a hybrid technology that offers the ability to measure basic physical and morphological characteristics (topography, rotational state, and density) of a small body from a single fast flyby, without requiring months in orbit. In addition, the imaging LADAR provides key flight navigation information including range, altitude, hazard/target avoidance, and closed-loop landing/fly-by navigation information. The Near Laser Ranger demonstrated many of these capabilities as part of the NEAR mission. The imaging LADAR scales the concept of a laser ranger into a full 3D imager. Imaging LADAR systems combine laser illumination of the target (which means that imaging is independent of solar illumination and the image SNR is controlled by the observer), with laser ranging and imaging (producing high resolution 3D images in a fraction of the time necessary for a passive imager). The technical concept described below alters the traditional design space (dominated by pulsed LADAR systems) with the introduction of a pseudo-noise (PN) coded continuous wave (CW) laser system which allows for variable range resolution mapping and leverages enormous commercial investments in high power, long-life lasers for telecommunications.

Optimization of spaceborne laser absorption spectroscopy sensor using parameter design

A number of gases present in the atmosphere play roles of interest to various parties. These are CO2 for its impact on understanding of global sources and sinks of Carbon, CH4 and H2O and their importance for global climate change, HCl and its importance in chemical processes. A space-borne sensor using multiple-wavelength Laser Absorption Spectroscopy (LAS) and mature CW fiber telecom lasers can address the critical questions concerning present and future patterns in these gases. The sensor identified above was designed from the outset using Taguchi Robust design techniques because of the need to adjust to varying science measurement requirements and technology capability as well as achieving optimum performance for optimum cost. The results describe a sensor with a SNR of 150 with a power aperture product of 3.92 watts-m2 on the absorption line is sufficient to meet the science requirements of 0.5% accuracy for determining the column density of CO2.