This paper provides an overview of the active optical technology developments supporting the Earth Science Division at
NASA. It summarizes key results from a multiyear NASA investment program aimed at enabling new Earth science
measurement capabilities, and a special program focused upon developing new techniques in the 1- and 2-micron
wavelengths and improving reliability and longevity of future NASA active sensing instruments. Examples for Earth
Science measurements such as atmospheric composition, altimetry, wind profiles, ozone levels, and vegetation change
The increasing use of lidar remote sensing systems in the limited power environments of unmanned aerial vehicles and
satellites is motivating laser engineers and designers to put a high premium on the overall efficiency of the laser
transmitters needed for these systems. Two particular examples upon which we have been focused are the lasers for the
ICESat-2 mission and for the Laser Vegetation Imaging Sensor-Global Hawk (LVIS-GH) system. We have recently
developed an environmentally hardened engineering unit for the ICESat-2 laser that has achieved over 9 W of 532 nm
output at 10 kHz with a wall plug efficiency to 532 nm of over 5%. The laser has a pulse width of <1.5 ns and an M2 of
<1.5. For the LVIS-GH lidar, we recently delivered a 4.2 W, 2.5 kHz, 1064 nm laser transmitter that achieved a wall
plug efficiency of 8.4%. The laser has a pulse width of 5 ns and an M2 of 1.1 We provide an overview of the design and
environmental testing of these laser transmitters.
Proc. SPIE 8159, Critical laser technology developments and ESA space qualification approach in support of ESA's Earth observation missions, 815904 (14 September 2011); https://doi.org/10.1117/12.893587
In this paper, ESA's approach to lasers and detectors space evaluation and qualification will be explored. ESA has its
own international qualification system, the ESCC system. This system guarantees reliability, assurance and quality of
components, and hence a successful space mission. An overview of the ESCC (European Space Component
Coordination) system, as well as the relevant ECSS (European Cooperation for Space Standards) related standards
addressing components and hybrid qualification will be given. These standards are being constantly updated, through
well structured working groups, constantly coming up with new ways of qualifying space components. These components
are themselves constantly changing in terms of material, technology, and manufacturing processes.
The development of advanced Lidar systems for space applications and their evaluation by airborne or ground based test
campaigns is an important strategic element of the ESA Earth Observation Programme. These systems depend on robust
and reliable lasers and detector at their core function. Since the early eighties, ESA has been supporting the
development of the critical subsystems of any Lidar, i.e. lasers and detectors. Several missions, involving different kinds
of lidars, provide the requirements to be addressed in the Lidar risk mitigation activities. They also present a challenge
concerning their space qualification and reliability assurance. These missions are: ADM-Aeolus flying ALADIN a
Doppler Wind Lidar; EarthCARE embarking ATLID an Atmospheric Backscatter Lidar; three missions studied for their
feasibilities: WALES, A-SCOPE and ACCURATE, all using Differential Absorption Lidar in different ways to measure
respectively profiles of water vapour, total column of CO2 and greenhouse gases in an occultation geometry.
The BepiColombo Laser Altimeter (BELA) is one of 11 instruments aboard ESA's Mercury Planetary Orbiter (MPO)
scheduled for launch in 2014. BELA will record the surface profile of the planet while orbiting around it at a distance of
400km to 1500km1. The altimetry data constitute an important prerequisite for a number of remote sensing and
observation techniques residing on the same orbiter. The BELA instrument comprises a laser transmitter and a receiver
part, the design of the former is being presented and discussed in this paper. The laser transmitter encompasses a pair of
diode-pumped, actively Q-switched Nd:YAG rod oscillators which have been miniaturized, light-weighted and
dimensioned for high electrical to optical efficiency. The key performance parameters of the laser will be presented.
Laser design trades which are relevant for a space mission to Mercury and the BELA instrument in particular are
discussed. An overview is given to the laser qualification programme which includes performance and environmental
tests. Test results are presented which have been recorded during the qualification test campaign currently in progress at
Carl Zeiss Optronics.
Laser remote sensing of the Earth from space offers many unique capabilities stemming from the unique properties of
lasers. Lidars make possible three-dimensional characterizations that enable new scientific understanding of the natural
processes that shape the planet's oceans, surface, and atmosphere. However, the challenges to further expand on these
successes remain complex. Operation of lidars from space is limited in part by the relatively low power available to the
lasers, the low signal scattered back to the instrument because of the large distance to the surface, and the need for
reliable and autonomous operation because of the significant investment required for satellites. The instrument
complexities are compounded by the diversity in the Earth scenes as well as the variability in albedo from cloud, ice,
vegetation, desert, or ocean, combined with the highly variable transmission of the laser beam through clouds, forest
canopy, or ocean surface and near-surface. This paper will discuss the development of a new approach to space-based
lidars that uses adaptive instrument techniques to dramatically enhance the capability of space-based lidars.
Methane is a powerful greenhouse gas. The radiative forcing caused by methane contributes significantly to the warming
of the atmosphere. To better understand the complex global Methane Cycle, it is necessary to apply space-based
measurements techniques in order to obtain global coverage at high precision
The Methane Remote Sensing Lidar Mission (MERLIN) is a joint French-German cooperation on a micro satellite
mission for space-based measurement of spatial and temporal gradients of atmospheric methane columns on a global
scale. MERLIN will be the first Integrated Path Differential Absorption LIDAR for methane monitoring from space. In
contrast to passive methane missions, the LIDAR instrument allows to retrieve methane fluxes at all-latitudes, allseasons
and during night as it is not relying on sunlight. First scientific studies show a substantial reduction of the prior
methane flux uncertainties in key observational regions when using synthetic MERLIN observations in the flux inversion
experiments. Furthermore, MERLIN observations can help to quantify and verify in scientific credible way national
emission reduction scenarios as formulated in the Kyoto protocol.
This paper reports on the present status of MERLIN and gives an overview on the joint mission concept with the German
LIDAR on the French satellite platform MYRIADE.
We report on the atmospheric pressure measurements using a fiber-based laser system using the
oxygen A-band at 765 nm. Remote measurements of atmospheric temperature and pressure are
required for a number of scientific applications including greenhouse gas monitoring, weather
prediction, and climate modeling.
The Jet Propulsion Laboratory Carbon Dioxide Laser Absorption Spectrometer (CO2LAS) utilizes Integrated Path
Differential Absorption (IPDA) at 2.05 μm to obtain CO2 column mixing ratios weighted heavily in the boundary layer.
CO2LAS employs a coherent detection receiver and continuous-wave Th:Ho:YLF laser transmitters with output powers
around 100 milliwatts. An offset frequency-locking scheme coupled to an absolute frequency reference enables the
frequencies of the online and offline lasers to be held to within 200 kHz of desired values. We describe results from
2009 field campaigns when CO2LAS flew on the Twin Otter. We also describe spectroscopic studies aimed at
uncovering potential biases in lidar CO2 retrievals at 2.05 μm.
Our goal is to develop and characterize optical measurement technology to enable accurate quantification of
greenhouse-gas emissions from distributed sources and sinks. We are constructing a differential absorption LIDAR
(DIAL) system that will be sensitive to the three primary greenhouse gases, carbon dioxide, methane, and nitrous oxide.
Our system uses a high energy optical parametric oscillator (OPO) operating from 1585 nm to 1646 nm. Here we
describe this OPO system and initial characterization of its output. The OPO uses a Rotated Image Singly-Resonant
Twisted RectAngle (RISTRA) design. The commercially available RISTRA cavity is machined from a solid block of
aluminum. The compact single piece cavity design requires no mirror adjustments and image rotation provides efficient
light conversion efficiency and excellent beam quality. The injection seeded OPO has demonstrated total output energy
of 50 mJ/pulse when pumped with 220 mJ/pulse of 1064 nm radiation. The pump laser has a repetition rate variable
from 1 Hz to 100 Hz and a temporal pulse width of 4.2 ns. In the current configuration the seed laser is locked to a mode
of the cavity.
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.
Analysis of data measured by the NASA Langley airborne High Spectral Resolution Lidar is presented focusing on
measurements over the ocean. The HSRL is a dual wavelength polarized system (1064 and 532 nm) with the inclusion of
a molecular backscatter channel at 532 nm. Data from aircraft flights over the Pamlico Sound out to the Atlantic Ocean,
over the Caribbean west of Barbados, and off the coast of Barrow, Alaska are evaluated. Analysis of the data
demonstrates that the molecular channel detects the presence of water due to its ability to differentiate the Brillouin-
Mandelshtam spectrum, i.e. the scattering spectrum of water, from the Rayleigh/Mie spectrum. The characteristics of the
lidar measurements over water, land, ice, and mixed ice/water surfaces are examined. Correlations of the molecular
channel lidar signals with bathymetry (ocean depth) and extraction of attenuation from the HSRL lidar measurements are
presented and contrasted with ocean color data.
This paper describes the results of a series of airborne observations of sardine schools off the coast of California in the
fall of 2010. The lidar system used a linearly-polarized transmitter and a single receiver that was sensitive to the
backscattered light in the orthogonal polarization. The aircraft was also equipped with a camera to photograph schools.
The camera had a broader swath than the lidar, so was able to see more of the schools at the surface. However, the lidar
detected schools much deeper in the water, was not hampered by waves and sun glare, and could survey at night. The
combination of lidar and photographs proved to be a very powerful survey tool for sardines, since the latter was able to
identify surface targets that appear very similar to fish schools in the lidar return. Examples of these include floating
mats of kelp and ship wakes.
In this paper the numerical simulation results of the Doppler lidar measurements for high horizontal spatial resolution
corresponding grid cell sizes of 1×1 km and 3×3 km are presented. It is shown that the variances, which characterize the
measurement uncertainty of components of mean wind velocity, depend strongly on state of the atmospheric turbulence
and the number and sizes of grid cell. Also the variances are the complex functions of the signal-to-noise ratio, VAD
sector scan angle, elevation angle, and direction sensing. The measurement uncertainty of component of mean wind
velocity U decreases with increasing cell number in the direction sensing of East and for horizontal spatial resolution of
1×1 km. But the measurement uncertainty increases with increasing cell number for resolution equal to 3×3 km. The
variance for the component U is a maximum and the component V has a minimum uncertainty of measurement in the
directions of North and South. The variance for the component U is a minimum and the component V has a maximum
measurement uncertainty in the directions of East and West. The variance for the components U and V have the same
values in the directions of North-East, North-West, South-East, and South-West.
The Supercontinuum (SC) generation during femtosecond laser pulse filamentation with various central wavelengths
in fused silica is investigated by numerical solution of nonlinear Schroedinger equation. Material dispersion of the
medium is considered due to Sellmeier formula. Nonmonotonic dependence of spectral intensity on wavelength in
anti-Stokes wing for anomalous group velocity dispersion (GVD) region (λ0 = 1900 nm) was found. There is a local
minimum in SC spectrum from 800 nm to 1200 nm, and there is also a local maximum in SC spectrum from 400 nm
to 700 nm. We suppose such modification of pulse spectrum during filamentation process to be caused by
interference modulation of SC spectrum in presence of anomalous GVD.
In this paper a wind sensing lidar utilizing a Frequency Stepped Pulse Train (FSPT) is demonstrated. One of the
advantages in the FSTP lidar is that it enables direct measurement of wind speed as a function of distance from
the lidar. Theoretically the FSPT lidar continuously produces measurements as is the case with a CW lidar, but
at the same time with a spatial resolution, and without the range ambiguity originating from e.g. clouds. The
FSPT lidar utilizes a frequency sweeping source for generation of the FSPT. The source generates a pulse train
where each pulse has an optical carrier frequency shifted a set quantity relative to the carrier frequency of the
previous pulse. In the scheme presented here, the measured frequency depends on the distance from which the
signal originates. The measured frequency is related to the Doppler frequency shift induced by the wind and an
integer number of frequency shifts corresponding to a specific distance. The spatial resolution depends on the
repetition rate of the pulses in the pulse train. Directional wind measurements are shown and compared to a
CW lidar measurement. The carrier to noise ratio of the FSPT lidar compared to a CW lidar is discussed as
well as the fundamental differences between the two systems. In the discussion we describe the most dominant
noise sources in our system and what influences these have on the FSPT lidar's ability to measure under different
Airborne LiDAR data have become cost-effective to produce at local and regional scales across the United States and
internationally. These data are typically collected and processed into surface data products by contractors for state and
local communities. Current algorithms for advanced processing of LiDAR point cloud data are normally implemented in
specialized, expensive software that is not available for many users, and these users are therefore unable to experiment
with the LiDAR point cloud data directly for extracting desired feature classes. The objective of this research is to
identify and assess automated, readily implementable GIS procedures to extract features like buildings, vegetated areas,
parking lots and roads from LiDAR data using standard image processing tools, as such tools are relatively mature with
many effective classification methods. The final procedure adopted employs four distinct stages. First, interpolation is
used to transfer the 3D points to a high-resolution raster. Raster grids of both height and intensity are generated. Second,
multiple raster maps - a normalized surface model (nDSM), difference of returns, slope, and the LiDAR intensity map -
are conflated to generate a multi-channel image. Third, a feature space of this image is created. Finally, supervised
classification on the feature space is implemented. The approach is demonstrated in both a conceptual model and on a
complex real-world case study, and its strengths and limitations are addressed.
Proc. SPIE 8159, Modeling of a tilted pressure-tuned field-widened Michelson interferometer for application in high spectral resolution lidar, 81590Q (14 September 2011); https://doi.org/10.1117/12.899406
High spectral resolution lidars (HSRLs) designed for aerosol and cloud remote sensing are increasingly being deployed
on aircraft and called for on future space-based missions. The HSRL technique relies on spectral discrimination of the
atmospheric backscatter signals to enable independent, unambiguous retrieval of aerosol extinction and backscatter. A
compact, monolithic field-widened Michelson interferometer is being developed as the spectral discrimination filter for
an HSRL system at NASA Langley Research Center. The Michelson interferometer consists of a cubic beam splitter, a
solid glass arm, and an air arm. The spacer that connects the air arm mirror to the main part of the interferometer is
designed to optimize thermal compensation such that the frequency of maximum interference can be tuned with great
precision to the transmitted laser wavelength. In this paper, a comprehensive radiometric model for the field-widened
Michelson interferometeric spectral filter is presented. The model incorporates the angular distribution and finite cross
sectional area of the light source, reflectance of all surfaces, loss of absorption, and lack of parallelism between the airarm
and solid arm, etc. The model can be used to assess the performance of the interferometer and thus it is a useful tool
to evaluate performance budgets and to set optical specifications for new designs of the same basic interferometer type.
Scannerless laser imaging radar will be the trend of laser imaging radar in future because it has several advantages of
high frame rate, wide field of view, small size and high reliability owing to giving up mechanical scanner. A scannerless
gain-modulated three-dimensional laser imaging radar is developed: Our system consists of a pulsed laser which is
capable of generating 100mJ pulses with a pulse width of 10ns and a center wavelength of 532 nm, and a receiver which
is a digital CCD sensor coupled to a GEN II intensifier with a 10nm bandwidth optical filter. The homogenized light
beam passes through a diverging lens to flood illuminate the targets. The return light is collected by a Nikon camera lens
and amplified by the image intensifier which is electronically driven and can be set to exponentially modulated gain or
constant gain. The CCD sensor can record a 12 bit gray-level image with a resolution of 780×582 pixels at a 50 Hz frame
rate. For a range image of the target can be extracted by processing an intensity image with exponentially modulated gain
and an intensity image with constant gain, the range image is acquired at a 25 Hz frame rate. During our outdoor
experiment, the range image of the targets at 500m is acquired with 2m range accuracy and the range image of the targets
at about 1 kilometer is acquired with 5m range accuracy in daytime.