Showing papers by "Charles E. Miller published in 2008"

Orbiting Carbon Observatory: Inverse method and prospective error analysis

Abstract: [1] The objective, design, and implementation of the OCO inverse method are presented The inverse method is the algorithm which finds the profile-weighted mean mixing ratio, XCO2, which best fits the measured spectrum, given a “forward model” which calculates the spectrum for a given atmospheric state, surface, and instrument properties Minimizing bias among comparative values of XCO2 is a critical objective The algorithm uses an “optimal,” maximum a posteriori inverse method, with weak a priori constraint, and employs a state vector containing atmospheric and surface properties expected to vary significantly between soundings An extensive operational characterization and error analysis will be employed, producing quantities designed to aid atmospheric modelers in use of the OCO data In particular, comparison to inverse models of surface CO2 flux will require use of the OCO column averaging kernel and a priori state vector An off-line error analysis has also been developed for more detailed error studies, and its use is illustrated by prospective application to case studies of nadir observations in summer and winter at three sites Uncertainties due to noise, geophysical variability, and spectroscopic parameters are considered in detail At low and midlatitudes, the single-sounding errors due to these sources are expected to be ∼07–08 ppm for high-sun conditions and ∼15–25 ppm for low sun (winter) Errors from the same sources in semimonthly regional averages are predicted to be <1 ppm for all conditions

Spectroscopic database of CO2 line parameters: 4300–7000 cm−1

Abstract: A new spectroscopic database for carbon dioxide in the near infrared is presented to support remote sensing of the terrestrial planets (Mars, Venus and the Earth). The compilation contains over 28,500 transitions of 210 bands from 4300 to 7000 cm−1 and involves nine isotopologues: 16O12C16O (626), 16O13C16O (636), 16O12C18O (628), 16O12C17O (627), 16O13C18O (638), 16O13C17O (637), 18O12C18O (828), 17O12C18O (728) and 18O13C18O (838). Calculated line positions, line intensities, Lorentz half-width and pressure-induced shift coefficients for self- and air-broadening are taken from our recent measurements and are presented for the Voigt molecular line shape. The database includes line intensities for 108 bands measured using the McMath–Pierce Fourier transform spectrometer located on Kitt Peak, Arizona. The available broadening parameters (half-widths and pressure-induced shifts) of 16O12C16O are applied to all isotopologues. Broadening coefficients are computed using empirical expressions that have been fitted to the experimental data. There are limited data for the temperature dependence of widths and so no improvement has been made for those parameters. The line intensities included in the catalog vary from 4×10−30 to 1.29×10−21 cm−1/(molecule cm−2) at 296 K. The total integrated intensity for this spectral interval is 5.9559×10−20 cm−1/(molecule cm−2) at 296 K.

NASA Orbiting Carbon Observatory: measuring the column averaged carbon dioxide mole fraction from space

Abstract: 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 ~03 to 05% (1 to 2 ppm) on regional scales every month

High-Precision Pressure Shifting Measurement Technique Using Frequency-Stabilized Cavity Ring-Down Spectroscopy

Abstract: We describe a high-precision method for measuring pressure shifting of absorption lines. The technique involves the acquisition of high-resolution spectra using a cavity ring-down spectrometer whose length is continuously locked to a frequency-stabilized reference laser over a range of sample pressures. We discuss a relatively large correction arising from the pressure-dependence of dispersion in the cavity modes, and we demonstrate pressure shifting measurements in air for transitions in the 16 O 2 A -band. Pressure shifts in the range - 0.011 to - 0.007 cm - 1 atm - 1 are reported. We measured relative positions of line centers to within 70 kHz and determined pressure shifting coefficients over a 5 kPa pressure range with relative uncertainties approximately equal to 1.0%, which constitutes a five-fold improvement over previous measurements.

Sensor-web Operations Explorer (SOX) for Earth Science Air Quality Mission Concepts

Abstract: Future air quality missions will face significant measurement strategy design and implementation challenges. Characterizing the atmospheric state and its impact on air quality requires observations of trace gases (e.g., ozone [O3], carbon monoxide [CO], nitrogen dioxide [NO2], sulfur dioxide [SO2]), aerosols (e.g., size and shape distributions, composition), clouds (e.g., type, height, sky coverage), and physical parameters (e.g., temperature, pressure, humidity) across temporal and spatial scales that range from minutes to days and from meters to > 10,000 km. Validating satellite measurements is another major challenge, and it requires well organized and orchestrated sub-orbital sensor web deployments. No single sensor, instrument, platform, or network can provide all of the information necessary to address this issue. Constellations of spacecraft, integrated air-borne campaigns, and distributed sensor networks have been actively pursued to achieve the needed multi-dimensional observation coverage. However, these complicated sensor webs must address how to formulate the complex design trade space, how to explore the trade space rapidly, how to establish evaluation metrics, and how to coordinate observations optimally. The Sensor-web Operations Explorer (SOX) research task under the NASA Earth Science Technology Office addresses these challenges by creating a virtual sensor-web experiment framework that can support orbital and sub-orbital observation system simulation experiment.

Sensor-web operations explorer

Abstract: Understanding the atmospheric state and its impact on air quality requires observations of trace gases, aerosols, clouds, and physical parameters across temporal and spatial scales that range from minutes to days and from meters to more than 10,000 kilometers. Observations include continuous local monitoring for particle formation; field campaigns for emissions, local transport, and chemistry; and periodic global measurements for continental transport and chemistry. Understanding includes global data assimilation framework capable of hierarchical coupling, dynamic integration of chemical data and atmospheric models, and feedback loops between models and observations. The objective of the sensor-web system is to observe trace gases, aerosols, clouds, and physical parameters, an integrated observation infrastructure composed of space-borne, air-borne, and in-situ sensors will be simulated based on their measurement physics properties. The objective of the sensor-web operation is to optimally plan for heterogeneous multiple sensors, the sampling strategies will be explored and science impact will be analyzed based on comprehensive modeling of atmospheric phenomena including convection, transport, and chemical process. Topics include system architecture, software architecture, hardware architecture, process flow, technology infusion, challenges, and future direction.

Linking Molecular- and Atomic-Frequency Standards with Cavity Ring-Down Spectroscopy

Abstract: We report a new method for measuring absorption transition frequencies using frequency-stabilized cavity ring-down spectroscopy. We determined absolute frequencies of O2A-band transitions using saturation spectroscopy of39K and demonstrated combined uncertainties < 1 MHz.