Dr. William S. Heaps Profile

Dr. William S. Heaps

Headm Laser & Electro-Optics at NASA Goddard Space Flight Ctr

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Publications (17)

Proceedings Article | 30 September 2011 Paper

New broadband lidar for greenhouse carbon dioxide gas sensing in the Earth's atmosphere

Elena Georgieva, William Heaps, Wen Huang

Proceedings Volume 8182, 81820H (2011) https://doi.org/10.1117/12.897552

KEYWORDS: LIDAR, Carbon dioxide, Absorption, Temperature metrology, Fabry–Perot interferometers, Receivers, Sensors, Earth's atmosphere, Atmospheric sensing, Carbon dioxide lasers

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Proceedings Article | 21 August 2009 Paper

Interferometric sensor for plant fluorescence

E. Georgieva, W. Heaps, E. Middleton, P. K. Campbell, L. Corp

Proceedings Volume 7454, 74540X (2009) https://doi.org/10.1117/12.825340

KEYWORDS: Luminescence, Sensors, Vegetation, Fabry–Perot interferometers, Interferometry, Reflectivity, Signal to noise ratio, Carbon, Absorption, Remote sensing

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We present preliminary design studies and modeling results for a new system for the assessment of vegetation photosynthetic function, especially carbon uptake. Plant health and carbon uptake efficiency are of key consideration in assessing global productivity, biomass, changes in land cover and carbon dioxide flux. Chlorophyll fluorescence (ChlF) measurements are critical for understanding photosynthetic functioning, plant environmental stress responses and direct assessments of plant health. Plant ChlF occurs predominately in two broad emission bands in the red and infrared regions of the spectrum. Unfortunately, the fluorescence signal from vegetation is much weaker than, and obscured by, the reflected signal. This limitation can be overcome by acquiring ChlF measurements in atmospheric absorption lines. The Interferometric Sensor for Plant Fluorescence (ISPF) will measure plant ChlF using the Fraunhofer Line Discrimination approach. Fabry-Perot (FP) etalons will be used to restrict the measurement to radiation in the Solar Fraunhofer lines (SFL). An advantage of the proposed sensor design is that it will collect measurements using two sets of SFL at the same time. This technique increases the optical throughput producing a larger signal to noise ratio (SNR). The instrument is designed to have two channels for two different spectral regions. Each channel will have two sub-channels, one defined by a prefilter (Reference, Ref) and the other having a tunable FP etalon. The first subchannel (the Ref) will cover a relatively broad spectral range to include at least two Fraunhofer lines but for which the fluorescence signal will represent only a small fraction of total reflected light. The second subchannel will use a FP interferometer to restrict the detected light to include only the selected SFL where the ChlF in-filling is significant. A small change in the fluorescence will then produce an insignificant change in the Ref subchannel but a relatively large change in signal from the FP subchannel. Changes in albedo or clouds will affect both subchannels proportionally so that the ratio of FP/Ref will be sensitive only to ChlF and almost insensitive to other parameters. The ISPF sensor will measure the fluorescence energy emitted by vegetation under natural sunlight. Advantages of the sensor over other designs are that it is passive (i.e., does not require an external illumination source), has simple structure and can be manufactured in a rugged, monolithic form that has no moving parts.

Proceedings Article | 15 October 2008 Paper

Broadband lidar technique for precision CO2 measurement

Wm. Heaps

Proceedings Volume 7111, 711102 (2008) https://doi.org/10.1117/12.802624

KEYWORDS: Fabry–Perot interferometers, Carbon dioxide, Absorption, LIDAR, Sensors, Carbon dioxide lasers, Light emitting diodes, Atmospheric sensing, Optical amplifiers, Signal detection

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Proceedings Article | 20 August 2008 Paper

Novel laser approach for remote sensing of atmospheric CO2 column

E. Georgieva, E. Wilson, W. Heaps

Proceedings Volume 7081, 70811G (2008) https://doi.org/10.1117/12.802718

KEYWORDS: Carbon dioxide, Fabry–Perot interferometers, Absorption, Sensors, Carbon dioxide lasers, LIDAR, Atmospheric laser remote sensing, Atmospheric sensing, Fabry–Perot interferometry, Carbon

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We present preliminary experimental results, sensitivity measurements and discuss our new CO₂ lidar system under development. The system is employing an erbium-doped fiber amplifier (EDFA), superluminescent light emitting diode (SLED) as a source and our previously developed Fabry-Perot interferometer subsystem as a detector part. Global measurement of carbon dioxide column with the aim of discovering and quantifying unknown sources and sinks has been a high priority for the last decade. The goal of Active Sensing of CO₂ Emissions over Nights, Days, and Seasons (ASCENDS) mission is to significantly enhance the understanding of the role of CO₂ in the global carbon cycle. The National Academy of Sciences recommended in its decadal survey that NASA put in orbit a CO₂ lidar to satisfy this long standing need. Existing passive sensors suffer from two shortcomings. Their measurement precision can be compromised by the path length uncertainties arising from scattering within the atmosphere. Also passive sensors using sunlight cannot observe the column at night. Both of these difficulties can be ameliorated by lidar techniques. Lidar systems present their own set of problems however. Temperature changes in the atmosphere alter the cross section for individual CO₂ absorption features while the different atmospheric pressures encountered passing through the atmosphere broaden the absorption lines. Currently proposed lidars require multiple lasers operating at multiple wavelengths simultaneously in order to untangle these effects. Our current goal is to develop an ultra precise, inexpensive new lidar system for precise column measurements of CO₂ changes in the lower atmosphere that uses a Fabry-Perot interferometer based system as the detector portion of the instrument and replaces the narrow band laser commonly used in lidars with the newly available high power SLED as the source. This approach reduces the number of individual lasers used in the system from three or more to one-considerably reducing the risk of failure. It also tremendously reduces the requirement for wavelength stability in the source putting this responsibility instead on the Fabry-Perot subsystem.

Proceedings Article | 20 August 2008 Paper

New differential Fabry-Perot radiometer for remote sensing measurements of column CO2, O2, H2O and other atmospheric trace gases

W. Heaps, E. Georgieva, E. Wilson

Proceedings Volume 7081, 70810K (2008) https://doi.org/10.1117/12.794995

KEYWORDS: Fabry–Perot interferometers, Carbon dioxide, Oxygen, Absorption, Gases, Sun, Atmospheric sensing, Sensors, Remote sensing, Satellites

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A new type of remote sensing instrument based upon the Fabry-Perot interferometric technique has been developed at NASA's Goddard Space Flight Center. Fabry-Perot interferometry (FPI) is a well known, powerful spectroscopic technique and one of its many applications is to be used to measure greenhouse gases and also some harmful species in the atmosphere. With this technique, absorption of particular species is measured and related to its concentration. A solid Fabry-Perot etalon is used as a frequency filter to restrict the measurement to particular absorption bands of the gas of interest. With adjusting the thickness of the etalon that separation (in frequency) of the transmitted fringes can be made equal to the almost constant separation of the gas absorption lines. By adjusting the temperature of the etalon, which changes the index of refraction of its material, the transmission fringes can be brought into nearly exact correspondence with absorption lines of the particular species. With this alignment between absorption lines and fringes, changes in the amount of a species in the atmosphere strongly affect the amount of light transmitted by the etalon and can be related to gas concentration. The instrument that we have developed detects the absorption of various atmospheric trace gases in direct or reflected sunlight. It can be used as ground based, airborne and satellite sensor for gases such as carbon dioxide (1570 nm), oxygen (762 nm and 768 nm lines sensitive to changes in oxygen pressure and oxygen temperature) and water vapor (940 nm). Our current goal is to develop an ultra precise, inexpensive, ground based device suitable for wide deployment as a validation instrument for the Orbiting Carbon Observatory (OCO) satellite. We show measurements for CO₂ and, O₂, , compare our measurements to those obtained using other types of sensors and discuss some of the peculiarities that must be addressed in order to provide the very high quality column detection required for solving problems about global distribution of greenhouse gases and climatological models. The recent long term experimental data on CO₂ and O₂ detection in atmosphere using Fabry-Perot technique are presented and discussed.

Proceedings Article | 3 October 2007 Paper

Measurement of carbon dioxide column via space-borne laser absorption

William Heaps

Proceedings Volume 6750, 67500V (2007) https://doi.org/10.1117/12.746734

KEYWORDS: Absorption, Carbon monoxide, Carbon dioxide lasers, Gas lasers, Laser systems engineering, Fiber lasers, Temperature metrology, Carbon dioxide, Satellites, Spectroscopy

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Proceedings Article | 4 May 2007 Paper

Progress in laser risk reduction for 1 micron lasers at GSFC

William Heaps

Proceedings Volume 6550, 65500Y (2007) https://doi.org/10.1117/12.720340

KEYWORDS: Laser development, LIDAR, Laser applications, Diodes, Reliability, Semiconductor lasers, Space operations, Laser systems engineering, Frequency conversion, Atmospheric laser remote sensing

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SPIE Journal Paper | 1 November 2006

Total column oxygen detection using a Fabry-Perot interferometer

Elena Georgieva, Emily Wilson, Mariusz Miodek, William Heaps

OE, Vol. 45, Issue 11, 115001, (November 2006) https://doi.org/10.1117/12.10.1117/1.2387878

KEYWORDS: Fabry–Perot interferometers, Oxygen, Absorption, Atmospheric modeling, Temperature metrology, Clouds, Atmospheric particles, Solar radiation, Optical engineering, Earth's atmosphere

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Proceedings Article | 7 September 2006 Paper

Precise measurement of CO2 from space using Fabry-Perot based optical setup: current status and development

E. Georgieva, E. Wilson, W. Heaps

Proceedings Volume 6296, 62961G (2006) https://doi.org/10.1117/12.679653

KEYWORDS: Fabry–Perot interferometers, Sun, Absorption, Carbon monoxide, Solids, Satellites, Sensors, Mars, Oxygen, Earth's atmosphere

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The FPICC (Fabry-Perot Interferometer for Column CO₂) is a new instrument developed under the Instrument Incubator Program that uses a novel technique for measuring the absorption of CO₂ sunlight reflected from the Earth. The optical setup consists of three channels. The first channel is built to measure carbon dioxide by using a solid Fabry-Perot etalon to restrict the measurement to light in CO₂ absorption bands. The second and third channels focus on the O₂ A band (759-771 nm) composed of about 300 absorption lines, which vary in strength and width according to pressure and temperature. We performed measurements using solid Fabry-Perot etalons with different FSR and different pre-filters. We demonstrated the instrument's significant capability to detect CO₂ and O₂ in laboratory, as well as in ground based and airborne experiments. The initial tests indicate that when the instrument is used with a sun tracker the sensitivity for CO₂ detection is 2.1 ppm in one second average, and the sensitivity to the oxygen column pressure changes is as low as 0.88 mbar. The reduced sensitivity for the airborne experiments arises because the atmospheric scattering processes make the path length more variable and uncertain. One solution to this problem is to use the glint reflection from water surfaces. For this purpose we design and perform a theoretical study to build a different version of the FPICC instrument to be used on a satellite orbiting the Earth and working in a glint mode. This Fabry-Perot based technique is applicable to other species as well. For example one could use the FPICC instrument for fractionations measurements of the stable carbon isotope (¹³C/¹²C). The instrument can be used to study the atmosphere of Mars, which consists primarily of CO₂. A theoretical study and design of a version of the instrument for Mars for CO₂ and CH₄ measurements will be presented. We report results on the recent calibration of the instrument, recent data from ground tests at Goddard, design versions, and theoretical models for the Earth and Mars instruments.

Proceedings Article | 23 August 2005 Paper

Atmospheric column CO2 and O2 absorption based on Fabry-Perot etalon for remote sensing

E. Georgieva, E. Wilson, M. Miodek, W. Heaps

Proceedings Volume 5882, 58820G (2005) https://doi.org/10.1117/12.612287

KEYWORDS: Fabry–Perot interferometers, Carbon monoxide, Absorption, Oxygen, Atmospheric sensing, Signal to noise ratio, Earth's atmosphere, Temperature metrology, Prisms, Sensors

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Proceedings Article | 12 January 2005 Paper

AROTAL: results from two arctic campaigns

Thomas McGee, Laurence Twigg, Walter Hoegy, John Burris, William Heaps, Grant Sumnicht, Chris Hostetler

Proceedings Volume 5653, (2005) https://doi.org/10.1117/12.578959

KEYWORDS: LIDAR, Ozone, Aerosols, Raman spectroscopy, Telescopes, Satellites, Ultraviolet radiation, Clouds, Backscatter, Raman scattering

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Proceedings Article | 30 December 2004 Paper

Ultra-precise measurement of CO2 from space

William Heaps, Stephan Kawa, Elena Georgieva, Emily Wilson

Proceedings Volume 5652, (2004) https://doi.org/10.1117/12.578521

KEYWORDS: Fabry–Perot interferometers, Carbon monoxide, Absorption, Oxygen, Atmospheric sensing, Remote sensing, Sun, Refractive index, Temperature metrology, Earth's atmosphere

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The experimental data on CO₂ and O₂ detection in atmosphere using Fabry-Perot technique are presented. The atmosphere's irradiance measurements are an important tool for the remote sensing study. We show results from lab, ground and flight testing of a new instrument called FPICC (Fabry-Perot Interferometer for Column CO₂) which is intended for a very precise measurements of atmospheric carbon dioxide and oxygen. The optical setup consists of three channels. The first channel is built to measure the carbon dioxide. This channel operates using the reflected sunlight off the ground and solid Fabry-Perot etalon to restrict the measurement to light in CO₂ absorption bands. The free spectral range of the etalon is calculated to be equal to the almost regular spacing between the CO₂ spectral bands located near 1,571 μm, R band, where CO₂ absorption is significant. The precise alignment of the transmission peaks of the Fabry-Perot etalon to the CO₂ absorption lines is achieved through altering the refractive index of the material (fused silica) using its temperature dependence. The second and third channels foucs on the O₂ A band (759 - 771 nm) composed of about 300 absorption lines, which vary in strength and width according to pressure and temperature. We performed measurements using solid Fabry-Perot etalons with different FSR and two different pre-filters. The first pre-filter selects a spectral range around 762 nm which is between the P and R branches, where the absorption coefficient is insensitive to temperature, but is sensitive to pressure changes and therefore to the variations in the O₂ column. The second pre-filter is selecting several absorption bands between 765 and 770 nm, which are more sensitive to temperature changes. The experimental data presented show excellent agreement with our theoretical expectations. They are recorded at different gas pressures, temperatures and different weather conditions. Some of the major advantages of the optical setup are its compactness, high sensitivity, high signal-to-noise ratio, and stability.

Proceedings Article | 26 October 2004 Paper

Experimental data on O2 absorption using Fabry-Perot-based optical setup for remote sensing atmospheric observations

Elena Georgieva, Emily Wilson, Mariusz Miodek, William Heaps

Proceedings Volume 5542, (2004) https://doi.org/10.1117/12.559891

KEYWORDS: Fabry–Perot interferometers, Absorption, Oxygen, Clouds, Atmospheric particles, Temperature metrology, Scattering, Atmospheric optics, Remote sensing, Atmospheric sensing

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The experimental data on O₂ absorption using reflected sunlight and a passive Fabry-Perot technique are presented. The atmosphere's irradiance measurements are an important tool for the remote sensing study. In this work we focus on the O₂ A band (759-771 nm) composed of about 300 absorption lines, which vary in strength and width according to pressure and temperature. We performed measurements using solid Fabry-Perot etalons with different FSR and two different pre-filters. The first pre-filter selects a spectral range around 763 nm which is between the P and R branches, where the absorption coefficient is insensitive to temperature, but is sensitive to pressure changes and therefore to the variations in the O₂ column. The second pre-filter is selecting several absorption bands between 765 and 770 nm, which are more sensitive to temperature changes. The optical setup consists of two channels. Channel one measure the total reflected light, whereas channel two uses a solid substrate Fabry-Perot etalon to restrict measurement to light in the O₂ absorption bands. The ratio of the intensities detected by the two channels is sensitive to O₂ pressure change or temperature change depending of the spectral region and is a function of the air mass, solar zenith angle and altitude. The experimental data presented shows excellent agreement with our theoretical expectations. They were recorded at different gas pressures and temperatures, and also at various weather conditions. The goal of the experiment is to demonstrate that variations of the column density of the O2 can be detected using a solid Fabry-Perot etalon. Results can be used for normalization of the other trace gases column densities, (to measure CO₂ column density) because the Oxygen is well mixed throughout most of the atmosphere (to an altitude of about 100 km) and can help to interpret the influence of scattering from aerosol and clouds, polarization of the reflected light, and the reflection properties of the surface. Some of the major advantages of our optical setup are its compactness, high sensitivity, high signal-to-noise ratio and stability.

Proceedings Article | 3 November 2003 Paper

Experimental data on CO2 detection using Fabry-Perot-based optical setup for atmospheric observations

Elena Georgieva, Emily Wilson, Mariusz Miodek, William Heaps

Proceedings Volume 5157, (2003) https://doi.org/10.1117/12.506008

KEYWORDS: Fabry–Perot interferometers, Carbon monoxide, Absorption, Atmospheric optics, Temperature metrology, Atmospheric sensing, Reflection, Solids, Sun, Refractive index

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Proceedings Article | 16 June 2003 Paper

Progress on passive sensor for ultraprecise measurement of carbon dioxide from space

William Heaps, S. Randolph Kawa

Proceedings Volume 4897, (2003) https://doi.org/10.1117/12.466163

KEYWORDS: Carbon monoxide, Absorption, Atmospheric sciences, Carbon, Carbon dioxide, Fabry–Perot interferometers, Temperature metrology, Atmospheric sensing, Climatology, Atmospheric modeling

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Proceedings Article | 8 April 2003 Paper

Simple Fabry-Perot-based instrument for surface pressure sensing from space

William Heaps

Proceedings Volume 4881, (2003) https://doi.org/10.1117/12.462997

KEYWORDS: Oxygen, Absorption, Satellites, Aerospace engineering, Fabry–Perot interferometers, Interferometers, Light scattering, Temperature metrology, Fabry–Perot interferometry, Sensors

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Proceedings Article | 21 March 2003 Paper

Laser risk reduction technology program for NASA's Earth Science Enterprise

Frank Peri, William Heaps, Upendra Singh

Proceedings Volume 4893, (2003) https://doi.org/10.1117/12.466071

KEYWORDS: Laser applications, LIDAR, Semiconductor lasers, Earth sciences, Transmitters, Ultraviolet radiation, Diodes, Nd:YAG lasers, Laser development, Aerosols

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Showing 5 of 17 publications

Conference Committee Involvement (1)

Lidar Remote Sensing for Industry and Environmental Monitoring V

9 November 2004 | Honolulu, Hawai'i, United States

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