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Randy Pollock

Bio: Randy Pollock is an academic researcher from Goodrich Corporation. The author has contributed to research in topics: Spectrometer & Imaging spectrometer. The author has an hindex of 6, co-authored 11 publications receiving 569 citations.

Papers
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Proceedings ArticleDOI
14 Oct 2004
TL;DR: In this article, 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.
Abstract: 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.

23 citations

Proceedings ArticleDOI
TL;DR: The status of the OCO instrument optical design is presented in this paper, where the optical bench assembly comprises three cooled grating spectrometers coupled to an all-reflective telescope/relay system.
Abstract: 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 the three spectral bands. The three bore sighted spectrometers allow the total column CO2 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.

14 citations

Journal ArticleDOI
TL;DR: In this article, the best focus of an optical system was established using a pupil-slicing technique using a set of optical displacement sensors measured by three piezo-actuated motors to adjust the tip, tilt, and piston of a focal plane assembly relative to the optical system.
Abstract: A technology for establishing best focus of an optical system is described. This technology was recently used to establish best focus of the Orbiting Carbon Observatory spectrometers while the instrument was undergoing thermal-vacuum testing. Three piezo-actuated motors were used to adjust the tip, tilt, and piston of a focal plane assembly relative to the spectrometer's optical system. A set of optical displacement sensors measured tip-tilt-piston throughout the focusing process. With best focus established and confirmed using a pupil-slicing technique, the corresponding sensor measurements were used to specify the geometry and dimensions of a precision-ground shim ring.

12 citations

Proceedings ArticleDOI
11 Feb 2002
TL;DR: The Wide Field-of-view Imaging Spectrometer (WFIS) as mentioned in this paper was developed for wide field hyperspectral imaging with several advantages over traditional scanning systems, such as increased wavelength coverage from the UV to the NIR and an increase in the field of view coverage to 120 degrees.
Abstract: This paper presents the status of the ongoing development of the laboratory Wide Field-of-view Imaging Spectrometer (WFIS) and the new engineering model WFIS. The design is shown to provide a unique solution to wide field hyperspectral imaging with several advantages over traditional scanning systems. Tests of the engineering model, funded under NASA's Instrument Incubator program, take the WFIS to the next level of technology readiness. The WFIS is based on a patented optical design intended for optical remote sensing of the earth and the earth's atmosphere in the hyperspectral-imaging mode. The design of the laboratory spectrometer and the initial test results obtained with it were presented at the 1999 SPIE Annual Meeting in Denver, Colorado (3759-32). Since that time, the laboratory unit has undergone several upgrades in the optical path and continues to be a pathfinder for the new engineering model instrument. The WFIS engineering model incorporates several improvements to provide increased wavelength coverage from the UV to the NIR and an increase in the field-of-view coverage to 120 degrees. It differs most significantly from the laboratory unit in that it is designed for flight. The status of the hardware, software, and the assembly of the engineering WFIS is discussed as well as an overview of the planned demonstration tests.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

6 citations


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Journal ArticleDOI
TL;DR: The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity, and molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth.
Abstract: This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.

7,638 citations

Journal ArticleDOI
TL;DR: The Greenhouse Gases Observing Satellite (GOSAT) monitors carbon dioxide and methane globally from space using two instruments using an ultraviolet (UV), visible, near infrared, and SWIR radiometer.
Abstract: The Greenhouse Gases Observing Satellite (GOSAT) monitors carbon dioxide (CO2) and methane (CH4) globally from space using two instruments. The Thermal and Near Infrared Sensor for Carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) detects gas absorption spectra of the solar short wave infrared (SWIR) reflected on the Earth's surface as well as of the thermal infrared radiated from the ground and the atmosphere. TANSO-FTS is capable of detecting three narrow bands (0.76, 1.6, and 2.0 μm) and a wide band (5.5-14.3 μm) with 0.2 cm−1 spectral resolution (interval). The TANSO Cloud and Aerosol Imager (TANSO-CAI) is an ultraviolet (UV), visible, near infrared, and SWIR radiometer designed to detect cloud and aerosol interference and to provide the data for their correction. GOSAT is placed in a sun-synchronous orbit 666 km at 13:00 local time, with an inclination angle of 98 °. A brief overview of the GOSAT project, scientific requirements, instrument designs, hardware performance, on-orbit operation, and data processing is provided.

734 citations

Journal ArticleDOI
TL;DR: In this article, the spectral signatures of three basic components: atmospheric absorption, surface reflectance, and fluorescence radiance are disentangled using a principal component analysis (PCA) approach.
Abstract: . Globally mapped terrestrial chlorophyll fluorescence retrievals are of high interest because they can provide information on the functional status of vegetation including light-use efficiency and global primary productivity that can be used for global carbon cycle modeling and agricultural applications. Previous satellite retrievals of fluorescence have relied solely upon the filling-in of solar Fraunhofer lines that are not significantly affected by atmospheric absorption. Although these measurements provide near-global coverage on a monthly basis, they suffer from relatively low precision and sparse spatial sampling. Here, we describe a new methodology to retrieve global far-red fluorescence information; we use hyperspectral data with a simplified radiative transfer model to disentangle the spectral signatures of three basic components: atmospheric absorption, surface reflectance, and fluorescence radiance. An empirically based principal component analysis approach is employed, primarily using cloudy data over ocean, to model and solve for the atmospheric absorption. Through detailed simulations, we demonstrate the feasibility of the approach and show that moderate-spectral-resolution measurements with a relatively high signal-to-noise ratio can be used to retrieve far-red fluorescence information with good precision and accuracy. The method is then applied to data from the Global Ozone Monitoring Instrument 2 (GOME-2). The GOME-2 fluorescence retrievals display similar spatial structure as compared with those from a simpler technique applied to the Greenhouse gases Observing SATellite (GOSAT). GOME-2 enables global mapping of far-red fluorescence with higher precision over smaller spatial and temporal scales than is possible with GOSAT. Near-global coverage is provided within a few days. We are able to show clearly for the first time physically plausible variations in fluorescence over the course of a single month at a spatial resolution of 0.5° × 0.5°. We also show some significant differences between fluorescence and coincident normalized difference vegetation indices (NDVI) retrievals.

536 citations

Journal ArticleDOI
TL;DR: In this paper, the authors describe the NASA Atmospheric CO2 Observations from Space (ACOS) XCO2 retrieval algorithm and its performance on highly realistic, simulated observations, and evaluate retrieval errors in the face of realistic clouds and aerosols, polarized non-Lambertian surfaces, imperfect meteorology, and uncorrelated instrument noise.
Abstract: . This work describes the NASA Atmospheric CO2 Observations from Space (ACOS) XCO2 retrieval algorithm, and its performance on highly realistic, simulated observations. These tests, restricted to observations over land, are used to evaluate retrieval errors in the face of realistic clouds and aerosols, polarized non-Lambertian surfaces, imperfect meteorology, and uncorrelated instrument noise. We find that post-retrieval filters are essential to eliminate the poorest retrievals, which arise primarily due to imperfect cloud screening. The remaining retrievals have RMS errors of approximately 1 ppm. Modeled instrument noise, based on the Greenhouse Gases Observing SATellite (GOSAT) in-flight performance, accounts for less than half the total error in these retrievals. A small fraction of unfiltered clouds, particularly thin cirrus, lead to a small positive bias of ~0.3 ppm. Overall, systematic errors due to imperfect characterization of clouds and aerosols dominate the error budget, while errors due to other simplifying assumptions, in particular those related to the prior meteorological fields, appear small.

473 citations

Journal ArticleDOI
TL;DR: A perspective on the contributions and future opportunities of the eddy covariance method is provided and the pros and cons of this method relative to other methods used to measure the exchange of trace gases between ecosystems and the atmosphere are discussed.
Abstract: The application of the eddy covariance flux method to measure fluxes of trace gas and energy between ecosystems and the atmosphere has exploded over the past 25 years. This opinion paper provides a perspective on the contributions and future opportunities of the eddy covariance method. First, the paper discusses the pros and cons of this method relative to other methods used to measure the exchange of trace gases between ecosystems and the atmosphere. Second, it discusses how the use of eddy covariance method has grown and evolved. Today, more than 400 flux measurement sites are operating world-wide and the duration of the time series exceed a decade at dozens of sites. Networks of tower sites now enable scientists to ask scientific questions related to climatic and ecological gradients, disturbance, changes in land use, and management. The paper ends with discussions on where the field of flux measurement is heading. Topics discussed include role of open access data sharing and data mining, in this new era of big data, and opportunities new sensors that measure a variety of trace gases, like volatile organic carbon compounds, methane and nitrous oxide, and aerosols, may yield.

395 citations