The second NASA Earth Venture Mission, Geostationary Carbon Cycle Observatory (GeoCarb), will provide measurements of atmospheric carbon dioxide (CO2), methane (CH4), carbon monoxide (CO), and solar-induced fluorescence (SIF) from Geostationary Orbit (GEO). The GeoCarb mission will deliver daily maps of column concentrations of CO2, CH4, and CO over the observed landmasses in the Americas at a spatial resolution of roughly 10 x 10 km. Persistent measurements of CO2, CH4, CO, and SIF will contribute significantly to resolving carbon emissions and illuminating biotic processes at urban to continental scales, which will allow the improvement of modeled biogeochemical processes in Earth System Models as well as monitor the response of the biosphere to disturbance. This is essential to improve understanding of the Carbon-Climate connection. In this paper, we introduce the instrument and the GeoCarb Mission, and we demonstrate the potential scientific contribution of the mission through a series of CO2 and CH4 simulation experiments. We find that GeoCarb will be able to constrain emissions at urban to continental spatial scales on weekly to annual time scales. The GeoCarb mission particularly builds upon the Orbiting Carbon Obserevatory-2 (OCO-2), which is flying in Low Earth Orbit.

The tropospheric Infrared Mapping Spectrometers (TIMS) operating at 2.33 and 4.68 µm were developed to demonstrate retrieval of atmospheric CO in several layers. In this presentation we describe the architecture of the 2.33 TIMS spectrometer, recap its development, develop its noise model, and validate that against TIMS demonstration data. We briefly describe a multi-channel geostationary space application, called geoCARB, of the TIMS technology and use the model to predict its signal to noise ratio (SNR).

Our companion paper ‘Progress in development of Tropospheric Infrared Mapping Spectrometers (TIMS): geostationary greenhouse gas (GHG) application’ describes geoCARB performance and science. Here we describe a geoCARB instrument design study leading to near PDR maturity. It is based on heritage geostationary (AIA and HMI on SDO, SBIRS GEO-1 and upcoming GLM on GOES-R as examples) and other (IRIS and NIRcam) flight instrumentation. Heritage work includes experience and well developed specifications for near a-thermal carbon fiber honeycomb composite optical benches and optical element mounting design forms that utilize a “family” of mounts for nearly any type of optical element. The geoCARB approach utilizes composite optical benches and bipod flexures to kinematically mount optics. Tooling for alignment and staking of all elements is integral to the design and is “removed before flight” for mass minimization. GeoCARB requires a cryogenic region for focal planes and spectrometers but front end optics and main structure are designed to run much warmer. A star tracker is used for geoCARB posteriori geolocation including pseudo-diurnal thermal distortion characterization. It is kinematically mounted by low conductance thermal isolators directly on to the low expansion high stiffness composite bench that defines the master optical surfaces including the scanning mirrors. The thermal load from the camera heads is routed away from the bench heat pipes. Use of kinematic mounting is advantageous for low thermal conduction designs. Honeycomb composites enable the design’s low thermal mechanical distortions.

Because it is a greenhouse gas, the detection of methane concentrations is a global issue. Additionally, the presence of methane is indicative of potential valuable petroleum and natural gas deposits. Therefore methane seep detection is useful for petroleum exploration around the world. The detection of methane, and other absorbing gases, over water is an issue for passive systems because one is seeking to detect an absorbing gas over an absorbing surface. The solution to this dilemma is to use the sun/sensor geometry for sun glint off of water to measure the absorbing gas over a reflecting surface, and therefore significantly increase the signal to noise of the measurement being taken. In September of 2010 Lockheed Martin performed a proof of concept by demonstrating from an airship over San Francisco Bay the capability of the Tropospheric Infrared Mapping Spectrometer's (TIMS) hyper spectral sensor to passively measure methane, CO, and water vapor over sunglint water. The Lockheed Martin prototype TIMS sensor system is a hyper spectral grating spectrometer instrument that operates in the 2.3 micron spectral region at 0.25 cm-1 resolution. The Lockheed Martin retrieval algorithm developed applies the kCARTA (kCompressed Atmospheric Radiative Transfer Algorithm) with Jacobians, with the HITRAN 2008 lineshape parameters, to retrieve the total column amount of atmospheric species along with the calibrated TIMS sensors radiometric input. A cell with known amount of methane was placed into the input to the TIMS to simulate atmospheric enhancements near the water surface. The amount in the cell was retrieved well within the uncertainty of 1% of the amount in the cell. Multi frame retrievals on data in which the cell was not placed into the input beam demonstrated 1% precision. In addition, in situ surface measurements were done over a landfill park, where measurements of methane were taken over known hotspots. This research allows for the future development of a system to measure methane, and other gases, for climate and petroleum exploration capabilities.

Resolution of important outstanding questions in air quality, climate change and ozone layer stability demands global observations of multiple chemical species with high horizontal and vertical resolution from the boundary layer to the stratopause. We present a mission concept that delivers the needed atmospheric composition observations, along with cloud ice and water vapor data needed for improvements in climate and weather forecasting models. The mission comprises ultraviolet and infrared nadir and microwave limb viewing instruments observing wide swaths each orbit.We review the scientific goals of the mission and the measurement capabilities this concept will deliver. We describe how precessing orbits offer significant improvements in temporal resolution and diurnal coverage compared to sun-synchronous orbits. Such improvements are needed to quantify the impact of critical "fast processes" such as deep convection on the composition and radiative properties of the upper troposphere, a region where water vapor and ozone are strong but poorly understood greenhouse gases.This concept can serve as the "Global Atmospheric Composition Mission" (GACM) recently recommended by the National Academy of Sciences decadal survey as one of 17 priority earth science missions for the coming decade.

Measurements of the column CH4, CO and CO2 are high priorities of the NPOESS Pre-Planned Product Improvement (P3I) data sets. Risk reduction for existing NPOESS instruments, including mitigation of daytime CO2 SWIR non-LTE effects, is also a high priority. We have proposed an NPOESS Instrument Of Opportunity (IOO) to address these priorities. It consists of two grating mapping spectrometers (GMSs). One that would acquire measurements with high spectral resolution Δv < 0.13 cm-1 of CH4, CO and H2O absorption lines in reflected sunlight in the VSWIR region 4281 to 4301 cm-1, and another for measurements with Δv < 0.30 cm-1 in the SWIR region 2355 to 2430 cm-1. The IOO will acquire spectra on a crosstrack swath from nadir to 55 degrees (about 1400 km on the ground) on footprints that are about 1.55 and 3.1 km on a side at nadir for the two GMS, respectively. The small footprint facilitates cloud screening, and identification of pollution hotspots. We use linear error analysis (LEA, based on the Rodgers [1] paper) to estimate the proposed IOO's performance. The LEA indicates that the IOO should be able to provide CH4 and CO column retrieval over sunlit land (and from ocean glitter when it is viewed) that satisfies or exceeds NPOESS P3I Environmental Data Records (EDRs) requirements in all aspects except refresh where the IOO would provide every two days vs the once per day requirement. Further, it shows the VSWIR IOO data when used in combination with the NPOESS Cross Track Infrared Sounder (CrIS) [2] data should provide: (a) CO profile data with sensitivity to CO in near surface air that is enhanced compared to that in the current TERRA-MOPITT, ACQUA-AIRS and AURA-TES data sets because these are limited to thermal infrared measurements that lack sensitivity to CO in near surface air layer where there is little contrast between the air temperature and the ground surface temperature, (b) CH4 profile with sensitivity in the near surface air layer that is crucial for identifying CH4 sources/sinks (c) and significant improvement in the CrIS retrieved humidity in the near surface layer of air. We show the SWIR IOO data can be used for CO2 column retrieval with near surface air layer sensitivity in the daytime. And also that in combination with CrIS SWIR data facilitates CO2 SWIR non-LTE mitigation that is required for advanced sounding quality temperature profile (TP) retrieval from CO2 SWIR data in daytime conditions. This provides risk reduction in case of degradation in the CrIS LWIR region data.

Precise measurements of CH 4 in a column of near surface air, and in partial columns above this, would be very valuable in identifying sources/sinks of atmospheric CH 4 , and its transport. For this purpose we have proposed a grating mapping spectrometer (GMS) for deployment as an Instrument of Opportunity (IOO) on the NPOESS that acquires data in the 2990 to 3050 cm -1 spectral region. It will provide measurements of CH 4 absorption of sunlight in the weaker CH 4 features in the region, and of thermal emission in the stronger CH 4 features in the region. It is the combination of the two that provides the vertical information. The IOO will acquire spectra on a crosstrack swath centered on nadir, and with 1/2 width of 55 degrees on each side of nadir (about 2800 km full width swath on the ground for a nominal 828 km satellite altitude). This with footprints that are about 3.1 km on a side at nadir. The small footprint facilitates cloud screening, and identification of CH 4 source hotspots. A capability to project the slit to nadir along the direction from satellite to sun will be utilized for over the ocean viewing in order to facilitate measurements in solar glitter. It will obtain spectra with resolution n -1 and sample spacing -1 . Based on the spectral characteristics and currently achievable very low-noise we do a linear error analysis (Rodgers, [1]) for the simultaneous retrieval of multi-column CH 4 , humidity, and surface parameters and 13 CH 4 total column. We show that useful multi-column CH 4 retrievals can be obtained, with good near surface sensitivity in sunlit conditions. We also show the 13 CH 4 column can be retrieved with precision better than 3%. Retrieval of 13 CH 4 column in the earth's atmosphere is analogous in difficulty to retrieval of the major CH 4 isotope column in the Martian atmosphere by a similar GMS deployed on a Mars orbiter. We show that H 2 O vertical information can be retrieved from these measurements and discuss the potential for ethane column retrieval.