Climate change and air quality are the most pressing environmental issues of the 21st century. Despite decades of research, the sources and sinks of key greenhouse gases remain highly uncertain [IPCC1] making quantitative predictions of atmospheric composition and their impacts. The Geostationary Remote Infrared Pollution Sounder (GRIPS) is a multi-purpose instrument designed to reduce uncertainty associated with atmospheric radiative forcing. GRIPS will measure will measure greenhouse gases and aerosols – two of the most important elements in the earth’s radiation budget. GRIPS will observe carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), - the carbon gases, nitrous oxide (N2O), water vapor and aerosols with unprecedented precision through the atmosphere. The GRIPS instrument uses gas filter correlation radiometry (GFCR) to detect reflected and thermal IR radiation to detect the gases and the reflected solar radiation in the visible and short-wave infrared bands for aerosols. GRIPS is designed to have sensitivity down to the Earth’s surface at ~2-8km nadir resolution. GRIPS can resolve CO2, CO, and CH4 anomalies in the planetary boundary layer and the free troposphere to quantify lofting, diurnal variations and longrange transport. With repeated measurements throughout the day GRIPS can maximize the number of cloud free measurements determining biogenic and anthropogenic sources, sinks, and fluxes. GRIPS is highly complementary to the Orbiting Carbon Observatory, OCO-2, the geostationary Tropospheric Emissions: Monitoring of Pollution (TEMPO) and Advanced Baseline Imager (ABI) and other existing and planned missions.
Over the last decade it has been established that medium- to long-range weather patterns are significantly affected by
stratospheric events, and it is well known that the severe storms are critically dependent on the winds aloft. However,
existing observations of the dynamical atmosphere above the cloud tops are sparse and irregular, and remote
measurements of upper atmospheric winds have historically proved challenging. Current numerical models must rely on
data from widely separated land-based instruments and satellite observations with modest precision and coverage. Even
less plentiful are observations of the neutral atmosphere above 100 km, despite the high potential impact of space
weather on global navigational and electrical systems. We present here a new instrument concept, the Doppler Wind
and Temperature Sounder (DWTS) that will enable global daily measurements of winds and temperature from 15 to 250
km with fine vertical and horizontal sampling. The measurement concept leverages the high spectral resolution
inherently available with gas-filter correlation radiometry. By exploiting the Doppler shifts resulting from a limbviewing
low Earth orbit satellite, DWTS spectrally resolves large ensembles of atmospheric emission features. From
this, we are able to extract horizontal wind vectors and kinetic temperature with unprecedented precision. Here we
review the DWTS measurement concept, present simulation results, and conclude by describing a low-cost operational
system that would quantify atmospheric dynamics from the lower stratosphere into the mid thermosphere for the first
time.
Climate change and air quality are the most pressing environmental issues of the 21st century. Despite decades of
research, the sources and sinks of key greenhouse gases remain highly uncertain [IPCC, 2007] making atmospheric
composition predictions difficult. The Geostationary Remote Infrared Pollution Sounder (GRIPS) will measure carbon
dioxide (CO2), carbon monoxide (CO), methane (CH4), and nitrous oxide (N2O) with unprecedented precision to
reduce substantially this uncertainty. The GRIPS instrument uses gas filter correlation radiometry (GFCR) to detect
reflected and thermal IR radiation from geostationary orbit. GRIPS is designed to haves sensitivity down to the Earth’s
surface at ~8 km nadir resolution. GRIPS can also resolve CO2, CO, and CH4 anomalies in the planetary boundary layer
and the free troposphere to quantify lofting, diurnal variations and long-range transport. With repeated measurements
throughout the day GRIPS can maximize the number of cloud free measurements determining biogenic and
anthropogenic sources, sinks, and fluxes. Finally, the GFCR technique is, to first order, insensitive to aerosols
interference. GRIPS is highly complementary to the Orbiting Carbon Observatory, OCO-2, and other existing and
planned missions.
We present the first results from a Digital Array Gas-correlation Radiometer (DAGR) prototype sensor, and discuss
applications in remote sensing of trace gases. The sensor concept is based on traditional and reliable Gas Filter
Correlation Radiometry (GFCR), but overcomes the limitations in solar backscatter applications. The DAGR sensor
design can be scaled to the size of a digital camera and is ideal for downlooking detection of gases in the boundary layer,
where solar backscatter measurements are needed to overcome the lack of thermal contrast in the IR. Ground-based
portable DAGR sensors can monitor carbon sequestration sites or industrial facilities. Aircraft or UAV deployment can
quickly survey large areas and are particularly well suited for gas leak detection or carbon monitoring. From space-based
platforms, Doppler modulation can be exploited to produce an extremely fine spectral resolution with effective
resolving power exceeding 100,000. Such space-based DAGR observations could provide near-global sensing of
climatically important species such as such as CO2, CO, CH4, O3 and N2O. Planetary science applications include
detection and mapping of biomarkers in the Martian atmosphere.
The Digital Array Gas Radiometer (DAGR) concept is based on traditional and reliable Gas Filter Correlation
Radiometry (GFCR) for remote trace gas detection and monitoring. GFCR sensors have been successful in many
infrared remote sensing applications. Historically however, solar backscatter measurements have not been as successful
because instrument designs have been susceptible to natural variations in surface albedo, which induce clutter and
degrade the sensitivity. DAGR overcomes this limitation with several key innovations. First, a pupil imaging system
scrambles the received light, removing nearly all spatial clutter and permitting a small calibration source to be easily
inserted. Then, by using focal plane arrays rather than single detectors to collect the light, dramatic advances in dynamic
range can be achieved. Finally, when used with the calibration source, data processing approaches can further mitigate
detector non-uniformity effects. DAGR sensors can be made as small as digital cameras and are well suited for
downlooking detection of gases in the boundary layer, where solar backscatter measurements are needed to overcome
the lack of thermal contrast in the IR. Easily integrated into a satellite platform, a space-based DAGR would provide
near-global sensing of climatically important species such as such as CO, CH4, and N2O. Aircraft and UAV
measurements with a DAGR could be used to monitor agricultural and industrial emissions. Ground-based or portable
DAGRs could augment early warning systems for chemical weapons or toxic materials. Finally, planetary science
applications include detection and mapping of biomarkers such as CH4 in the Martian atmosphere.
The Halogen Occultation Experiment (HALOE) operated in orbit for over 14 years, providing high quality measurements from the upper troposphere into the lower thermosphere. Since the quality of this data set depended on the long-term stability of the instrument, a series of analysis tests were designed to routinely monitor instrument performance. These tests evaluated possible changes in the gas cells, electronic gains, optical performance, and signal temperature dependencies. The gas cell stability was determined from an analysis of the Doppler shift signature in retrieved mixing ratios. Electronic gain stability was determined by instrument scans of the solar disk, each with different balance settings. Optical and tracking performance was also determined from solar scan data. The only statistically significant changes detected were: 1. a small methane gas cell change, causing less than 0.5% per decade change in retrieved methane, and 2. a small optical alignment change in the HF channel that only affects HF results below 25 kilometers. These detailed analyses indicate that the HALOE instrument remained stable throughout the mission, adding confidence to the long-term atmospheric trends deduced from HALOE products.
The Solar Occultation For Ice Experiment (SOFIE) was launched onboard the Aeronomy of Ice in the Mesosphere
(AIM) satellite on 25 April 2007, and began science observations on 14 May 2007. SOFIE conducts solar occultation
measurements in 16 spectral bands that are used to retrieval vertical profiles of temperature, O3, H2O, CO2, CH4, NO,
and polar mesospheric cloud (PMC) extinction at 11 wavelengths. SOFIE provides 15 sunrise and 15 sunset
measurements each day at latitudes from 65°-85°S and 65°-85°N. This work describes the SOFIE experiment and
shows preliminary retrieval results based on observations from the initial months on-orbit.
The Solar Occultation For Ice Experiment (SOFIE) is scheduled for launch onboard the Aeronomy of Ice in the
Mesosphere (AIM) satellite in March 2007. SOFIE is designed to measure polar mesospheric clouds (PMCs) and the
environment in which they form. SOFIE will conduct solar occultation measurements in 16 spectral bands that are used to retrieve vertical profiles of temperature, O3, H2O, CO2, CH4, NO, and PMC extinction at 10 wavelengths. Thirty
occultations are observed each day covering latitudes from 65° - 85°S and 65° - 85°N. The PMC measurements are
simultaneous with temperature and gas measurements that are unaffected by PMC signal. This data set will be the first
of its kind, and allow new advancements in the understanding of the upper mesosphere.
Accurate simultaneous retrievals of temperature and pressure are key to retrieving high quality mixing ratio profiles from occultation sensors. Equally important is accurate determination of the vertical separation between measurement points. Traditionally, these tasks are complicated by platform motion and CO2 model errors. We present a new approach that is independent of platform motion and CO2 concentration, using inexpensive modern 2D focal-plane arrays and an innovative refraction-angle measurement. This provides both accurate temperature retrievals and precise vertical separation of measurement samples, greatly improving the quality of mixing ratio retrievals. We show recent studies demonstrating the expected performance of the SOFIE instrument (Solar Occultation For Ice Experiment) to be launched as part of the AIM (Aeronomy of Ice Mission) in September 2006. This system will have the ability to retrieve accurate temperature, through mild particulate contamination (such as volcanic aerosol and cirrus) from cloud-top to stratopause, independent of mixing ratio knowledge. Additional CO2 absorption channels will provide retrieved temperature and CO2 mixing ratios through the mesosphere and into the lower thermosphere.
Accurate temperature and pressure profiles are the key to high quality retrievals from solar occultation measurements. For best results these profiles should be retrieved from measurements that have an identical field-of-view and are simultaneous, with companion measurements. We explore three general methods, corresponding implementation strategies and their major error sources. These methods include: 1) one or more channels sensing CO2 extinction, 2) a single channel using the oxygen A band, and 3) use of refraction angle measurements to infer temperature from density derivatives (limited to the stratosphere). It is shown that extraordinary results can be achieved if high precision solar tracking, and solar pointing knowledge, are accomplished.
Solar occultation measurements from satellite have been very successful at sounding the upper atmosphere from cloud-top to well into the mesosphere (e.g. HALOE, ATMOS, SAGE, POAM). The HALOE instrument achieves transmission precision of 4 X10-6 at 2 arcminute resolution (1.6 Km at the Earth limb) with the differential gas correlation technique. With modern detectors, high precision tracking, better throughput and differential broadband radiometry, achievable precision should approach 10-7 (~10-9 km-1 extinction) or better. We show that this will allow accurate sounding of CO2, O3, H2O and NO mixing ratios simultaneously with temperature and pressure well into the lower thermosphere. In addition, such precision could provide the first mapping of the Earth's cosmic dust layer.
Infrared multispectral sensors are being investigated as a means for day and night target detection. Infrared multispectral sensors would exploit high spectral band-to-band correlation to reject high background clutter. An infrared Fourier transform spectrometer-based field measurement system was used to collect spectral signature data of targets and desert scrub and sand backgrounds from a 100 foot tower at White Sands Missile Range. The measurements include target-to-background spectral contrast, subpixel targets, background spectral correlation, and background spatial power spectra. The measurements have been analyzed to determine multispectral signal-to-clutter ratios versus target, background, diurnal, and weather variations, background correlation versus temperature clutter variations, and spectral correlation versus spatial scale. These measurements contribute to the expanding target and background infrared hyperspectral signature database. The results of the analysis demonstrate the utility and robustness of infrared multispectral techniques for target detection.
A series of infrared hyperspectral field measurements was made at Wright Patterson Air Force Base and the U.S. Army White Sands Missile Range by the Joint Multispectral Program (JMSP) between November 1993 and June 1994. In these experiments, a highly sensitive Fourier transform spectrometer (FTS) was used to collect data from test panels, military and civilian vehicles, and various types of natural backgrounds. Post-collection data analyses are being conducted by the JMSP to assess the potential of thermal multispectral processing for detecting and classifying low-contrast ground targets in natural clutter environments. One target material of special interest is CARC paint, which is currently applied to U.S. Army vehicles in various colors to create woodland and desert camouflage patterns. CARC-painted test panels were observed in a wide variety of backgrounds and weather conditions during all of the JMSP experiments. It is shown here that certain fine-scale spectral features of this paint can support reliable two-color discrimination of CARC-coated test panels in different natural backgrounds, even under low contrast and high clutter conditions. The paper also examines environmental variations in two key parameters that determine spectral detectability; specifically, the observed target-background spectral contrast signature (which provides the required coloring), and the background spectral correlation (which provides for multiband clutter suppression).
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