Atmospheric methane trends over the last few years have been increasing at a rate of 7-12 parts per billion (ppb) per year after brief a pause in the first decade of this century. The reasons for the pause and subsequent increase remains unclear. Thus, there is a critical need for additional, precise and accurate methane observations to understand the natural and anthropogenic processes that drive the trends in atmospheric methane and to constrain its sources, and sinks. At NASA Goddard Space Flight Center (GSFC), in collaboration with Freedom Photonics Inc., we have been developing a lidar to measure atmospheric methane using Integrated Path Differential Absorption (IPDA) from an airborne platform as a precursor to a future space mission. In this paper we present the design of a laser transmitter operating at ~1651 nm based on a newly developed Distributed Bragg Grating (DBR) seed laser and an Optical parametric oscillator (OPO). The DBR is rapidly step-tuned over the methane absorption at several discrete wavelengths. This multi-wavelength approach enables us to sample the entire methane lineshape and reduce systematic errors.
The global and regional quantification of methane fluxes and identification of its sources and sinks has been highlighted as one of the goals of the NASA 2017 Earth Science Decadal Survey. Detecting methane from space and airborne platforms with an active (laser) remote sensing instrument presents several unique technology and measurement challenges. The instrument must have a single frequency, narrow-linewidth light source, and photon-sensitive detector at the right spectral region to make continuous measurements from orbit, day and night, all seasons and at all latitudes. It must have a high signal to noise ratio and must be relatively immune to biases from aerosol/cloud scattering, spectroscopic and meteorological data uncertainties, and instrument systematic errors.
At Goddard Space Flight Center (GSFC), in collaboration with industry, we have developed an airborne instrument to measure methane. Our instrument is a nadir-viewing lidar that uses Integrated Path Differential Absorption (IPDA), to measure methane near 1.65 μm. We sample the absorption line using multiple wavelengths from a narrow linewidth laser source and a sensitive photodetector. This measurement approach provides maximum information content about the CH4 column, and minimizes biases in the XCH4 retrieval.
In this paper, we will review our progress to date and discuss the technology challenges, options and tradeoffs to measure methane from space and airborne platforms.
NASA’s Goddard Space Flight Center has been developing lidar to remotely measure CO2 and CH4 in the Earth’s atmosphere. The ultimate goal is to make space-based satellite measurements with global coverage. We are working on maturing the technology readiness of a fiber-based, 1.57-micron wavelength laser transmitter designed for use in atmospheric CO2 remote-sensing. To this end, we are building a ruggedized prototype to demonstrate the required power and performance and survive the required environment.
We are building a fiber-based master oscillator power amplifier (MOPA) laser transmitter architecture. The laser is a wavelength-locked, single frequency, externally modulated DBR operating at 1.57-micron followed by erbium-doped fiber amplifiers. The last amplifier stage is a polarization-maintaining, very-large-mode-area fiber with ~1000 μm2 effective area pumped by a Raman fiber laser. The optical output is single-frequency, one microsecond pulses with >450 μJ pulse energy, 7.5 KHz repetition rate, single spatial mode, and < 20 dB polarization extinction.
Trace gases and their isotopic ratios in planetary atmospheres offer important but subtle clues as to the origins of a planet's atmosphere, hydrology, geology, and potential for biology. An orbiting laser remote sensing instrument is capable of measuring trace gases on a global scale with unprecedented accuracy, and higher spatial resolution that can be obtained by passive instruments.
For Earth we have developed laser technique for the remote measurement of the tropospheric CO2, O2, and CH4 concentrations from space. Our goal is to develop a space instrument and mission approach for active CO2 measurements. Our technique uses several on and off-line wavelengths tuned to the CO2 and O2 absorption lines. This exploits the atmospheric pressure broadening of the gas lines to weigh the measurement sensitivity to the atmospheric column below 5 km and maximizes sensitivity to CO2 changes in the boundary layer where variations caused by surface sources and sinks are largest. Simultaneous measurements of O2 column use a selected region in the Oxygen A-band. Laser altimetry and atmospheric backscatter can also be measured simultaneously, which permits determining the surface height and measurements made to thick cloud tops and through aerosol layers.
We use the same technique but with a different transmitter at 1.65 um to measure methane concentrations. Methane is also a very important trace gas on earth, and a stronger greenhouse gas than CO2 on a per molecule basis. Accurate, global observations are needed in order to better understand climate change and reduce the uncertainty in the carbon budget. Although carbon dioxide is currently the primary greenhouse gas of interest, methane can have a much larger impact on climate change. Methane levels have remained relatively constant over the last decade but recent observations in the Arctic have indicated that levels may be on the rise due to permafrost thawing. NASA’s Decadal Survey underscored the importance of Methane as a greenhouse gas and called for a mission to measure CO2, CO and CH4. Methane has absorptions in the mid-infrared (3.3 um) and the near infrared (1.65 um). The 3.3 um spectral region is ideal for planetary (Mars) Methane monitoring, but unfortunately is not suitable for earth monitoring since the Methane absorption lines are severely interfered with by water. The near infra-red overtones of Methane at 1.65 um are relatively free of interference from other atmospheric species and are suitable for Earth observations. The methane instrument uses Optical Parametric Generation (OPG) along with sensitive detectors to achieve the necessary sensitivity. Our instrument generates and detects tunable laser signals in the 3.3 or 1.65 um spectral regions with different detectors in order to measure methane on Earth or Mars. For Mars, the main interest in methane is its importance as a biogenic marker.
We report on an airborne demonstration of atmospheric methane (CH4) measurements with an integrated path differential absorption lidar using an optical parametric amplifier and optical parametric oscillator laser transmitter and sensitive avalanche photodiode detector. The lidar measures the atmospheric CH4 absorption at multiple, discrete wavelengths near 1650.96 nm. The instrument was deployed in the fall of 2015, aboard NASA’s DC-8 airborne laboratory along with an in situ spectrometer and measured CH4 over a wide range of surfaces and atmospheric conditions from altitudes of 2 to 13 km. We will show the results from our flights, compare the performance of the two laser transmitters, and identify areas of improvement for the lidar.
Atmospheric methane (CH4) is the second most important anthropogenic greenhouse gas with approximately 25 times the radiative forcing of carbon dioxide (CO2) per molecule. CH4 also contributes to pollution in the lower atmosphere through chemical reactions leading to ozone production. Recent developments of LIDAR measurement technology for CH4 have been previously reported by Goddard Space Flight Center (GSFC). In this paper, we report on a novel, high-performance tunable semiconductor laser technology developed by Freedom Photonics for the 1650nm wavelength range operation, and for LIDAR detection of CH4. Devices described are monolithic, with simple control, and compatible with low-cost fabrication techniques. We present 3 different types of tunable lasers implemented for this application.
We report on an airborne demonstration of atmospheric methane (CH4) measurements with an Integrated Path Differential Absorption (IPDA) lidar using an optical parametric oscillator (OPO) and optical parametric amplifier (OPA) laser transmitter and a sensitive avalanche photo detector. The lidar measures the CH4 absorption at multiple, discrete wavelengths around 1650.9 nm. In September 2015, the instrument was deployed on NASA’s DC-8 airborne laboratory and measured atmospheric methane over a wide range of topography and weather conditions from altitudes of 3 km to 13 km. In this paper, we will review the results from our flights, and identify areas of improvement.
Atmospheric methane (CH4) is the second most important anthropogenic greenhouse gas, with approximately 25 times the radiative forcing of carbon dioxide (CO2) per molecule. Yet, lack of understanding of the processes that control CH4 sources and sinks and its potential release from stored carbon reservoirs contributes significant uncertainty to our knowledge of the interaction between carbon cycle and climate change. At Goddard Space Flight Center (GSFC) we have been developing the technology needed to remotely measure CH4 from orbit. Our concept for a CH4 lidar is a nadir viewing instrument that uses the strong laser echoes from the Earth’s surface to measure CH4. The instrument uses a tunable, narrow-frequency light source and photon-sensitive detector to make continuous measurements from orbit, in sunlight and darkness, at all latitudes and can be relatively immune to errors introduced by scattering from clouds and aerosols. Our measurement technique uses Integrated Path Differential Absorption (IPDA), which measures the absorption of laser pulses by a trace gas when tuned to a wavelength coincident with an absorption line. We have already demonstrated ground-based and airborne CH4 detection using Optical Parametric Amplifiers (OPA) at 1651 nm using a laser with approximately 10 μJ/pulse at 5kHz with a narrow linewidth. Next, we will upgrade our OPO system to add several more wavelengths in preparation for our September 2015 airborne campaign, and expect that these upgrades will enable CH4 measurements with 1% precision (10-20 ppb).
NASA’s Goddard Space Flight Center (GSFC) is working on maturing the technology readiness of a laser transmitter designed for use in atmospheric CO2 remote-sensing. GSFC has been developing an airplane-based CO2 lidar instrument over several years to demonstrate the efficacy of the instrumentation and measurement technique and to link the science models to the instrument performance. The ultimate goal is to make space-based satellite measurements with global coverage. In order to accomplish this, we must demonstrate the technology readiness and performance of the components as well as demonstrate the required power-scaling to make the link with the required signal-to-noise-ratio (SNR). To date, all the instrument components have been shown to have the required performance with the exception of the laser transmitter. In this program we are working on a fiber-based master oscillator power amplifier (MOPA) laser transmitter architecture where we will develop a ruggedized package and perform the relevant environmental tests to demonstrate TRL-6. In this paper we will review our transmitter architecture and progress on the performance and packaging of the laser transmitter.
The Advanced Topographic Laser Altimeter System (ATLAS) will be the only instrument on the Ice, Cloud, and Land
Elevation Satellite -2 (ICESat-2). ICESat-2 is the 2nd-generation of the orbiting laser altimeter ICESat, which will
continue polar ice topography measurements with improved precision laser-ranging techniques. In contrast to the
original ICESat design, ICESat-2 will use a micro-pulse, multi-beam approach that provides dense cross-track sampling
to help scientists determine a surface's slope with each pass of the satellite. The ATLAS laser will emit visible, green
laser pulses at a wavelength of 532 nm and a rate of 10 kHz and will be split into 6 beams. A set of six identical,
thermally tuned optical filter assemblies (OFA) will be used to remove background solar radiation from the collected
signal while transmitting the laser light to the detectors. A seventh assembly will be used to monitor the laser center
wavelength during the mission. In this paper, we present the design and optical performance measurements of the
ATLAS OFA in air and in vacuum prior to their integration on the ATLAS instrument.
We demonstrate the airborne measurement of atmospheric methane using a pulsed lidar at 1650 nm using an integrated path differential absorption scheme. Our seeded nanosecond-pulsed optical parametric amplifier (OPA)-based instrument works up to the highest altitudes flown (<10 km). The obtained absorption profile is in good agreement with theoretical predictions based on the HITRAN database.
We report on the development effort of a nanosecond-pulsed optical parametric amplifier (OPA) for remote trace gas measurements for Mars and Earth. The OPA output has ∼500 MHz linewidth and is widely tunable at both near-infrared and mid-infrared wavelengths, with an optical-optical conversion efficiency of up to ∼39% . Using this laser source, we demonstrated open-path measurements of CH 4 (3291 and 1652 nm), CO 2 (1573 nm), H 2 O (1652 nm), and CO (4764 nm) on the ground. The simplicity, tunability, and power scalability of the OPA make it a strong candidate for general planetary lidar instruments, which will offer important information on the origins of the planet's geology, atmosphere, and potential for biology.
We report on ground and airborne atmospheric methane measurements with a differential absorption lidar using an
optical parametric amplifier (OPA). Methane is a strong greenhouse gas on Earth and its accurate global mapping is
urgently needed to understand climate change. We are developing a nanosecond-pulsed OPA for remote measurements
of methane from an Earth-orbiting satellite. We have successfully demonstrated the detection of methane on the ground
and from an airplane at ~11-km altitude.
At NASA's Goddard Space Flight Center we are developing next generation laser transmitters for future spaceflight,
remote instruments including a micropulse altimeter for ice-sheet and sea ice monitoring, laser spectroscopic
measurements of atmospheric CO2 and an imaging lidar for high resolution mapping of the Earth's surface. These laser
transmitters also have applicability to potential missions to other solar-system bodies for trace gas measurements and
surface mapping. In this paper we review NASA spaceflight laser transmitters used to acquire measurements in orbit
around Mars, Mercury, Earth and the Moon. We then present an overview of our current spaceflight laser programs and
describe their intended uses for remote sensing science and exploration applications.
At NASA's Goddard Space Flight Center, we are developing the next generation laser transmitters for future remote
sensing applications including a micropulse altimeter for ice-sheet monitoring, laser spectroscopic measurements and
high resolution mapping of the Earth's surface as well as potential missions to other planets for trace gas measurement
and mapping. In this paper we will present an overview of the spaceborne laser programs and offer insights into future
spaceborne lasers for remote sensing applications.
Trace gases in planetary atmospheres offer important clues as to the origins of the planet's hydrology, geology,
atmosphere, and potential for biology. We report on the development effort of a nanosecond-pulsed optical parametric
amplifier (OPA) for remote trace gas measurements for Mars and Earth. The OPA output light is single frequency with
high spectral purity and is widely tunable both at 1600 nm and 3300 nm with an optical-optical conversion efficiency of
~40%. We demonstrated open-path atmospheric measurements of CH4 (3291 nm and 1651 nm), CO2 (1573 nm), H2O
(1652 nm) with this laser source.
Many fundamental questions about planetary evolution require monitoring of the
planet's atmosphere with unprecedented accuracy at both high and low latitudes, over both
day and night and all seasons. Each planetary atmosphere presents its own unique challenges.
For the planets/moons that have relatively low surface pressure and low trace gas
concentrations, such as Mars or Europa, the challenge is to have enough sensitivity to
measure the trace gas of interest. For Earth, the challenge is to measure trace gases with very
high precision and accuracy in the presence of other interfering species.
An orbiting laser remote sensing instrument is capable of measuring trace gases on a global
scale with unprecedented accuracy, and higher spatial resolution that can be obtained by
passive instruments. For Mars, our proposed measurement uses Optical Parametric
Amplifiers (OPA) and Integrated Path Differential Absorption (IDPA) in the 3-4 um spectral
range to map various trace gas concentrations from orbit on a global scale. For earth, we
propose to use Erbium Doped Fiber Amplifier technology (EDFA) and IDPA at 1.57 and
OPA at 1.65 μm to measure carbon dioxide and methane concentrations respectively.
NASA Goddard Space Flight Center (GSFC) has been engaging in Earth and planetary science remote sensing
instruments development for many years. The latest instrument was launched in 2008 to the moon providing the most
detailed topographic map of the lunar surface to-date. NASA GSFC is preparing for several future missions, which for
the first time will perform active spectroscopic measurements from space. In this paper we will review the past, present
and future of space-qualified lasers for remote sensing applications at GSFC.
We report on the development effort of a nanosecond-pulsed seeded optical parametric generator (OPG) for remote trace
gas measurements. The seeded OPG output light is single frequency with high spectral purity and is widely tunable both
at 1600nm and 3300nm with an optical-optical conversion efficiency of ~40%. We demonstrated simultaneous tuning
over the methane (CH4) absorption line at idler wavelength, 3270.4nm, and carbon dioxide (CO2) absorption line at
signal wavelength, 1578.2nm. In this paper, we will also discuss open-path atmospheric measurements with this newly
developed laser source.
Single-photon avalanche photodiodes (SPADs) based on an improved structure were fabricated. Measurement
results show that SPADs with a sharp rising I-V and gain curves were obtained by controlling SPAD's
multiplication region thickness. The tunneling leakage current was reduced. Device's dark count rates (DCR) and
single photon detection efficiency (SPDE) were measured using our innovative gated current bias scheme under
different operating conditions to obtain a maximum SPDE. The experimental data demonstrated that SPADs'
performance can be improved by decreasing the difference between the breakdown voltage and the punch through
For the detection of single photons at 1.06 μm, silicon-based single photon avalanche diodes (SPADs) used at shorter
wavelengths have very low single photon detection efficiency (~1 - 2%), while InP/InGaAs SPADs designed for
telecommunications wavelengths near 1.5 μm exhibit dark count rates that generally inhibit non-gated (free-running)
operation. To bridge this "single photon detection gap" for wavelengths just beyond 1 μm, we have developed high
performance, large area (80 - 200 μm diameter) InP-based InGaAsP quaternary absorber SPADs optimized for
operation at 1.06 μm. We demonstrate dark count rates that are sufficiently low to allow for non-gated operation while
achieving detection efficiencies far surpassing those found for Si SPADs. At a detection efficiency of 10%, 80 μm
diameter devices exhibit dark count rates below 1000 Hz and photon counting rates exceeding 1 MHz when operated at