The Orbiting Carbon Observatory-2 (OCO-2) is this first NASA satellite designed to measure atmospheric carbon dioxide (CO2) with the accuracy, resolution, and coverage needed to detect CO2 sources and sinks on regional scales over the globe. OCO-2 was launched from Vandenberg Air Force Base on 2 July 2014, and joined the 705 km Afternoon Constellation a month later. Its primary instrument, a 3-channel imaging grating spectrometer, was then cooled to its operating temperatures and began collecting about one million soundings over the sunlit hemisphere each day. As expected, about 13% of these measurements are sufficiently cloud free to yield full-column estimates of the columnaveraged atmospheric CO2 dry air mole fraction, XCO2. After almost a full year in orbit, the XCO2 product is beginning to reveal some of the most robust features of the atmospheric carbon cycle, including the northern hemisphere spring drawdown, and enhanced values co-located with intense fossil fuel and biomass burning emissions. As the carbon cycle science community continues to analyze these OCO-2 data, information on regional-scale sources (emitters) and sinks (absorbers) as well as far more subtle features are expected to emerge from this high resolution, global data set.
The Orbiting Carbon Observatory is scheduled for launch from Vandenberg Air Force Base in California in January
2009. This Earth System Science Pathfinder (ESSP) mission carries and points a single instrument that incorporates 3
high-resolution grating spectrometers designed to measure the absorption of reflected sunlight by near-infrared carbon
dioxide (CO<sub>2</sub>) and molecular oxygen bands. These spectra will be analyzed to retrieve estimates of the column-averaged
CO<sub>2</sub> dry air mole fraction, X<sub>CO2</sub>. Pre-flight qualification and calibration tests completed in early 2008 indicate that the
instrument will provide high quality X<sub>CO2</sub> data. The instrument was integrated into the spacecraft, and the completed
Observatory was qualified and tested during the spring and summer of 2008, in preparation for delivery to the launch site
in the fall of this year. The Observatory will initially be launched into a 635 km altitude, near-polar orbit. The on-board
propulsion system will then raise the orbit to 705 km and insert OCO into the Earth Observing System Afternoon
Constellation (A-Train). The first routine science observations are expected about 45 days after launch. Calibrated
spectral radiances will be archived starting about 6 months later. An exploratory X<sub>CO2</sub> product will be validated and then
archived starting about 3 months after that.
Final assembly and integration of the Orbiting Carbon Observatory instrument at the Jet Propulsion Laboratory in
Pasadena, California is now complete. The instrument was shipped to Orbital Sciences Corporation in March of this
year for integration with the spacecraft. This observatory will measure carbon dioxide and molecular oxygen absorption
to retrieve the total column carbon dioxide from a low Earth orbit. An overview of the design-driving science
requirements is presented. This paper then reviews some of the key challenges encountered in the development of the
sensor. Diffraction grating technology, lens assembly performance assessment, optical bench design for manufacture,
optical alignment and other issues specific to scene-coupled high-resolution grating spectrometers for this difficult
science retrieval are discussed.
The NASA Orbiting Carbon Observatory (OCO) will make space-based measurements of atmospheric carbon dioxide (CO2) with the precision, resolution, and coverage needed to characterize regional scale CO2 sources and sinks and quantify their vari¬ability over the seasonal cycle. This mission will be launched in December 2008 and will fly in a 705 km altitude, 1:26 PM sun-synchronous orbit that provides complete coverage of the sunlit hemisphere with a 16-day ground track repeat cycle. OCO carries a single instrument designed to make co-boresighted spectroscopic measurements of reflected sunlight in near-infrared CO2 and molecular oxygen (O2) bands. These CO2 and O2 measurements will be combined to provide spatially resolved estimates of the column averaged CO2 dry air mole fraction, XCO2. The instrument collects 12 to 24 XCO2 soundings/second over the sunlit portion of the orbit, yielding 200 to 400 soundings per degree of latitude, or 7 to 14 million soundings every 16 days. Existing studies indicate that at least 10% of these soundings will be sufficiently cloud free to yield XCO2 estimates with accuracies of ~0.3 to 0.5% (1 to 2 ppm) on regional scales every month.
The NASA Orbiting Carbon Observatory (OCO) will make space-based measurements of atmospheric CO<sub>2</sub> with the precision, resolution, and coverage needed to characterize CO<sub>2</sub> sources and sinks on regional scales and quantify their variability over the seasonal cycle. This Earth System Science Pathfinder (ESSP) mission will be launched in late 2008 and will fly in a 705 km altitude, 1:26 PM sun-synchronous polar orbit that provides near-global coverage of the sunlit hemisphere with a 16-day ground track repeat cycle. OCO carries a single instrument that incorporates 3 high resolution grating spectrometers that will make boresighted measurements of reflected sunlight in near-infrared CO<sub>2</sub> and molecular oxygen (O<sub>2</sub>) bands. These measurements will be combined to provide spatially resolved estimates of the column-averaged CO<sub>2</sub> dry air mole fraction, XCO<sub>2</sub>. The instrument collects 12 to 24 X<sub>CO</sub><sub>2</sub> soundings/second over the sunlit portion of the orbit, yielding 200 to 400 soundings per degree of latitude, or 7 to 14 million soundings every 16 days. Thick clouds and aerosols will reduce the number of soundings available for X<sub>CO</sub><sub>2</sub> retrievals by 80-90%, but the remaining data is expected to yield XCO<sub>2</sub> estimates with accuracies of ~0.3 to 0.5% (1 to 2 ppm) on regional scales every month.
The Orbiting Carbon Observatory, OCO, is a NASA Earth System Science Pathfinder (ESSP) mission to measure the distribution of total column carbon dioxide in the earth's atmosphere from an earth orbiting satellite. NASA Headquarters confirmed this mission on May 12, 2005. The California Institute of Technology's Jet Propulsion Laboratory is leading the mission. Hamilton Sundstrand is responsible for providing the OCO instrument. Orbital Sciences Corporation is supplying the spacecraft and the launch vehicle. The optical design of the OCO is now in the detail design phase and efforts are focused on the Critical Design Review (CDR) of the instrument to be held in the 4th quarter of this year. OCO will be launched in September of 2008. It will orbit at the head of what is known as the Afternoon Constellation or A-Train (OCO, EOS-Aqua, CloudSat, CALIPSO, PARASOL and EOS-Aura). From a near polar sun synchronous (~1:18 PM equator crossing) orbit, OCO will provide the first space-based measurements of carbon dioxide on a scale and with the accuracy and precision to quantify terrestrial sources and sinks of CO<sub>2</sub>. The status of the OCO instrument optical design is presented in this paper. The optical bench assembly comprises three cooled grating spectrometers coupled to an all-reflective telescope/relay system. Dichroic beam splitters are used to separate the light from a common telescope into three spectral bands. The three bore-sighted spectrometers allow the total column CO<sub>2</sub> absorption path to be corrected for optical path and surface pressure uncertainties, aerosols, and water vapor. The design of the instrument is based on classic flight proven technologies.
The Orbiting Carbon Observatory (OCO) will measure the distribution of total column carbon dioxide in the Earth's atmosphere from an Earth-orbiting satellite. Three high-resolution grating spectrometers measure two CO2 bands centered at 1.61 and 2.06 μm and the oxygen A-band centered at 0.76 μm in the near infrared region of the spectrum. This paper presents the optical design and highlights the critical optical requirements flowed down from the scientific requirements. These requirements necessitate a focal ratio of f/1.9, a spectral resolution of 20,000, and precedence-setting requirements for polarization stability and the instrument line shape function. The solution encompasses three grating spectrometers that are patterned after a simple refractive spectrometer approach consisting of an entrance slit, a two-element collimator, a planar reflection grating, and a two-element camera lens. Each spectrometer shares a common field of view through a single all-reflective telescope. The light is then re-collimated and passed through a relay system, separating the three bands before re-imaging the scene onto each of the spectrometer entrance slits using an all-reflective inverse Newtonian re-imager.
The Oxygen A-band spectrometer breadboard was developed to demonstrate alignment and focus methodologies planned for the spectrometers to be used for the Orbiting Carbon Observatory (OCO). The OCO is a proposed Earth System Science Pathfinder (ESSP) mission to provide the first global CO<sub>2</sub> measurements from space with a relative accuracy of 1-ppm on scales of 2.5 × 10<sup>5</sup> km<sup>2</sup>. The flight system uses three refractive spectrometers to measure column CO<sub>2</sub> at 1.58 and 2.06-micrometers and column O<sub>2</sub> in the oxygen A-band at 0.76 micrometers. This paper describes a relatively fast, f/2, high resolution grating spectrometer breadboard designed, manufactured, and tested in less than 6 months. The breadboard successfully validates the optical design and alignment approach to be used for the three spectrometers that comprise the OCO instrument.
This work is a continuation of our theoretical analyses of the H<SUB>2</SUB>S Fourier-transform spectrum, recorded in Kitt Peak National Observatory, in 2000 - 11,000 cm<SUP>-1</SUP> spectral region. This time we deal with 4,500 - 5,600 cm<SUP>-1</SUP> spectral region where the first hexad of vibrational bands (nu) <SUB>1</SUB> plus (nu) <SUB>3</SUB>, 2(nu) <SUB>2</SUB> plus (nu) <SUB>3</SUB>, (nu) <SUB>1</SUB> plus 2(nu) <SUB>2</SUB>, 4(nu) <SUB>2</SUB>, 2(nu) <SUB>1</SUB>, 2(nu) <SUB>3</SUB> are placed. In comparison with the previous work significantly more precise vibrational-rotational energy levels of the analyzed vibrational states have been obtained from the spectrum assignment, which was performed with the use of special computer program. The parallel refinement of the rotational and dipole moments parameters allowed us to make reliable predictional calculations and assign not only strong lines, included in combination differences, but a weak single lines also. Finally 1052 precise vibrational- rotational energy levels for all six members of the hexad have been derived in comparison with 542 from our previous work.
The present paper is a continuation of our effort to analyze high resolution H<SUB>2</SUB>S absorption spectra from 2000 to 11,500 cm<SUP>-1</SUP> using the Fourier-transform spectrometer at Kitt Peak. Previously, the observed band centers for 30 states were assigned and fitted in a vibrational analyses, and local mode behavior was demonstrated in four bands near 1 micrometer. Here we present the first (2(nu) <SUB>2</SUB>, (nu) <SUB>1</SUB> and (nu) <SUB>3</SUB> near 4 micrometer) and second 3(nu) <SUB>2</SUB>, (nu) <SUB>1</SUB> plus (nu) <SUB>2</SUB> and (nu) <SUB>2</SUB> plus (nu) <SUB>3</SUB> near 2.7 micrometer) triad system.
An absorption spectra of H<SUB>2</SUB>S have been recorded at 0.006 and 0.012 cm<SUP>-1</SUP> resolution in 2000 - 9000 cm<SUP>-1</SUP> spectral region using the Kitt Peak national observatory Fourier-Transform spectrometer. Two spectra of H<SUB>2</SUB>S at 1.49 Torr and at 9.99 Torr have been measured using non-linear least squares fitting to obtain line positions, intensities and self- broadening widths. The spectra identification has been made and twelve new bands have been assigned. The vibrational constants have been fitted to all known band centers.