Space-based Lidar Remote Sensing Techniques and Emerging Technologies

The High-Spectral-Resolution Lidar (HSRL) Pathfinder Mission concept is designed to provide HSRL measurements at 532 nm and elastic backscatter lidar measurements at 1064 nm. The instrument is based on Clio, the HSRL that was descoped from NASA’s Atmosphere Observing System (AOS) mission due to cost constraints. The NASA Langley Research Center (LaRC) developed the HSRL Pathfinder concept as an example of a lower-cost mission to advance the technology and demonstrate the measurement capability originally planned for AOS. Cost savings are achieved via a Class-D instrument development approach and some reductions in performance from the original Clio design. Despite these changes, the HSRL Pathfinder Mission promises to provide valuable observations for advancing studies of aerosol and cloud radiative effects, cloud microphysics, aerosol-cloud interaction, aerosol transport and speciation, and air quality. The design also enables scientifically important observations of depth-resolved ocean subsurface optical properties, snow water equivalent, and seasonal sea ice, making HSRL Pathfinder a truly multifunctional lidar mission.

Selected for development in 1998 and launched together with CloudSat in 2006, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission terminated science operations in the summer of 2023 after completing 17 years of on-orbit observations. As one of NASA’s Earth System Science Pathfinder missions, CALIPSO was truly a pathfinder. CALIPSO observations provided a new perspective on clouds and aerosol and have not only met but far exceeded the original objectives of the mission. Many unanticipated findings and data applications have been discovered along the way. Flying with many other remote sensing instruments, as part of the A-train constellation, stimulated the discovery of numerous retrieval synergies between lidar and other sensors. This paper describes how the CALIPSO mission came to be, discusses some of the early choices made by the CALIPSO team that shaped the mission, and some of the challenges facing the team in developing the first-ever global climatologies of aerosol and cloud based on lidar observations.

A new airborne coherent Doppler Wind Lidar (DWL) instrument has been implemented leveraging NASA's development of the 2-micron Wind-Space Pathfinder (Wind-SP) lidar transceiver. A technology development project, Wind-SP refined and demonstrated numerous components required for a coherent-detection space wind lidar instrument. Aerosol Wind Profiler (AWP) transitioned this transceiver into an airborne wind lidar capable of providing full 3-D wind vector retrievals. AWP operates with laser pulse energy and repetition rate combination required for high spatial and vertical resolution wind profiling from space. Operation from aircraft platforms will yield very strong signal return required for detailed process studies at <2 km spatial and <100 m vertical resolution under most conditions. AWP will serve as NASA’s wind calibration and validation instrument for future space-based wind observations over the coming decades, while also providing data supporting space wind lidar simulation studies. The AWP instrument is introduced and preliminary results from recent AWP demonstration flights are presented.

Global wind measurements are essential for numerical weather prediction (NWP), climate studies, and various meteorological studies. Current space-based passive sensors and micro sensors have large coverage and high temporal resolution but low vertical resolution. The Doppler Wind Llidar (DWL) is a useful technique for wind measurement. JAXA studies the feasibility of a future space-based coherent DWL (CDWL) for global wind profile observation. The mission concept of the space-based CDWL is designed to have one look for line-of-sight (LOS) wind measurement at an off-nadir angle of 35° at an azimuth angle of 90° (270°) along satellite track. The candidate altitude and orbit of the satellite are 300 km and dawn-dusk sun-synchronous polar orbit. The forecast impacts of both 1.5- and 2-µm space-based DWL were evaluated using the operational global data assimilation system. The data assimilation experiments were conducted in August in 2018 to assess overall impact and seasonal dependence. It is found that the two space-based DWL have positive impact on NWP. Relative forecast error reduction for 1.5- and 2-µm space-based DWLs can be expected to about 3 and 2%, respectively. Compared to the 2-µm DWL experiment, 1.5-µm DWL experiment had a feature that the number of data usage is larger in the lower layer and less in the upper layer. The future space-based CDWL will fill the gap of the current global wind observing systems and contribute to the improvement of the initial conditions for NWP, atmospheric dynamics and phenomena, and various meteorological researches.

Aerosols and clouds play critical roles in the Earth’s weather, air quality, and climate system at multiple spatiotemporal scales. To achieve better characterization of spatiotemporal variability of aerosols and clouds, we need new sensors and architectures that creatively utilize advanced SmallSat technologies. A compact backscatter lidar has been designed to improve spatiotemporal sampling and fit the current mass, volume, and power limits of a SmallSat. A version of this lidar concept, called the Atmospheric Lidar Instrument for Clouds and Aerosol Transport (ALICAT), is being considered for the NASA Atmosphere Observing System (AOS) mission. ALICAT adds capabilities and improves performance compared to previous space-based lidars. ALICAT is mature, as it draws heritage from the Cloud-Aerosol Transport System (CATS) and maturation/testing through Earth Science Technology Office (ESTO) investments.

Clouds play a crucial role in the Earth’s energy budget, but their feedback is still uncertain. A thorough grasp of clouds, encompassing their cover, vertical arrangement, and optical characteristics, is vital for comprehending and predicting the Earth's energy balance and climate. Satellite observations have been providing a continuous monitoring of clouds, with active sounders being of particular importance because of their vertical and horizontal resolution and accuracy. But, comparing the clouds retrieved from different space-borne lidars is challenging because of differences in wavelength, pulse energy, detector type, local time of overpass, and so on. This study presents an approach to merge clouds measured by the space-borne lidar ALADIN/Aeolus (355 nm), with clouds retrieved from the CALIPSO lidar observations (532 nm). The method involves compensating for the instrumental differences to attain comparable cloud datasets. This sets a path for integrating future lidars, such as ATLID/EarthCare, into the global lidar cloud record.

A pulsed 2-mm Integrated Path Differential Absorption (IPDA) lidar was developed at NASA Langley Research Center for high-accuracy and high-precision measurements of atmospheric carbon dioxide (CO2). The instrument targets the R30 CO2 absorption line and implements high-energy tunable on-line transmitter and advanced HgCdTe avalanche photodiode receiver. During 2019 airborne validation campaign, the IPDA was tested over the ocean for retrieving the weighted-average column dry-air volume mixing ratio of CO2 (XCO2) from 4.5 km altitude. XCO2 measurement resulted in 404.43 ± 1.23 ppm using 10 s average, as compared to 405.49 ppm from prediction models. This translates to 0.26% and 0.30% relative accuracy and precision, respectively. Performance models were updated to scale the IPDA technology assuming operation from a space platform. Results present XCO2 measurements using the instrument capabilities considering different target scenarios for Earth’s surface. This demonstrates the potential for the IPDA technique and technology to achieve sustained global CO2 measurement.

MOLI is Japan’s first Earth observation mission to observe the ground elevation and forests canopy height with the complementary measurement of an imager and lidar. The mission equipment is operated in space through the compartment where ISS-JEM astronauts operate, which helps mitigate the launch environment compared to typical satellite-borne instrument. Consequently, we are conducting prototyping and evaluation tests of lasers and power supplies. Building upon the research findings, we have transitioned to the preparatory phase for launching the mission and are actively engaged in project development and launch operations, despite the approaching ISS operation deadline. Furthermore, ongoing research is focused on developing advanced functionalities based on the results obtained from MOLI.

Spaceborne lidar is an important instrument to measure the global atmospheric CO2 column concentrations and aerosol profiles with high accuracy. Atmospheric environment monitoring satellite (AEMS, also named as DQ-1) Aerosol and Carbon dioxide Detection Lidar (ACDL) is a novel spaceborne lidar, which integrates two lidar systems in a set of lidar setup, using a 1572 nm integrated path laser differential absorption (IPDA) method to measure the global CO2 column concentrations, and using a 532 nm high spectrum resolution lidar (HSRL) method to measure the vertical profiles of aerosol and cloud, which was firstly successfully validated. AEMS was launched on April 16th, 2022 and ACDL has worked more than one year continuously. The global carbon dioxide column concentrations (XCO2) from 82° N to 82° S over land and sea on daytime and nighttime are presented. The ACDL XCO2 measurements are compared with TCCON sites XCO2 data. For the first time, the global XCO2 with accuracy of better than 1 ppm and aerosol profiles with accuracy of better than 20% are obtained with spaceborne active sensor.

We report development progress of a Concurrent Artificially-intelligent Spectrometry and Adaptive Lidar System (CASALS) for topography swath mapping from space. The beam scanning was demonstrated by fast wavelength tuning and grating dispersion, and near quantum limited performance was measured at 1550 nm. A 1040 nm CASALS prototype is being developed for Earth science. The laser is rapidly tuned across 13 nm and carved into 2-ns pulses to scan 256 tracks. At the grating-spectrometer-based receiver, returns from each track are filtered spatially and spectrally and imaged onto a HgCdTe APD-array. The detected signals are time-division-multiplexed to only two high-speed analog-to-digital converters and range-gated to reduce data volume. The design can be adapted for gapless sub-meter resolution lunar swath mapping at 1550 nm. 3D imaging of landing site with 4 M footprints per second is enabled by inserting a 4-Hz 2D steering mirror. The lidar can also perform navigation measurements up to 100 km.

A new generation of satellites using novel LiDAR concept could provide more accurate monitoring of greenhouse gas emissions, helping to improve our understanding of the role of human activity in climate change. The use of satellite constellations for this purpose has several advantages. First, it would allow for near-global coverage, providing a more complete picture of emissions than is possible with ground-based monitoring. Second, the use of LiDAR would allow for more accurate measurements, as it can provide aerosols and subvisible clouds extinction and scattering properties, and measure local winds correcting the bias and error in Radiative Transfer algorithms. This would be a valuable tool for understanding and mitigating climate change, as it would provide more accurate data on emissions from different regions and sectors. It could also help to identify areas where emissions reductions are most urgently needed. The main goal of the project is to explore an approach of deploying a network of new data sources for GHG monitoring with high temporal and special resolution. The target parameters are 50 m resolution for CH4 and CO2 with 4 passes per day over the area of interest. This will enable new emissions monitoring applications to combat the climate crisis by delivering L2 level data about greenhouse gas emissions concentrations on the predefined location. The deployment of such a system would require significant investment, but the benefits would be considerable. It is therefore worth considering as part of the efforts to combat climate change. This paper will explore the state of the art in this area and discuss future directions.

The ESA HERA mission (to be launched October 2024) provides an in-depth characterisation as follow-up from the impact of the moon of the Didymos asteroid system by NASA’s DART mission in September 2022. HERA, thanks to many scientific instruments, plans to characterize the Didymos binary asteroid system after impact to help our understanding for planetary defence. In specific, the Lidar instrument (PALT-Planetary Altimeter) is a time-of-flight ranging payload, operating at 1.535 µm, that will have dual use for both science and GNC (Guidance, Navigation and Control) purposes. PALT will assist in the shape determination of Didymos and its moon, Dimorphos, contribute to the mass determination of Dimorphos, and measure its orbital state and wobble. PALT will augment the datasets of HERA’s imaging payloads and radio science experiment. As a GNC sensor, PALT will support the autonomous navigation for very close asteroid flybys. PALT is a development from EFACEC (Portugal and Romania), Synopsis Planet (Portugal), Eventech (Latvia) and INOE(Romania). The HERA spacecraft is being built by OHB System AG in Bremen, Germany.

Over the past years, with the support of the European Space Agency (ESA) and in collaboration with the Fondazione Bruno Kessler (FBK), CSEM has developed a direct time-of-flight flash lidar technology that now reaches a TRL 4. The lidar prototype is designed for space exploration (landing) and servicing (rendezvous) applications as well as underwater imaging. It provides a 3D image of 128 × 128 pixels with a field-of-view of 4 to 20°. The system fits inside a 20 cm cube, weighs less than 6.5 kg, and draws less than 60 W. First, this work reviews the current prototype and its performances. Second, technological trade-offs, and a comparison against state-of-the-art scanning lidars is provided. Third, an outlook towards future developments following a New Space approach and benefiting from synergies with complementary applications will be presented.

Kongsberg Defence & Aerospace (KDA) and SINTEF are developing a flash-LIDAR for use in space and specifically for landing applications. The baseline is a compact 5 kg design without moving parts. The technology is based on time-of-flight (ToF) measurement of emitted laser pulses with the use of a Mega pixel CMOS camera. Each short high energy laser pulse illuminates the complete target area. By selecting different delay times for the camera gating and through real time processing of the sensor output, a three-dimensional image of the scene is generated. The technology is tolerant to sunlight illuminating the landing site. A narrow band optical filter is utilized to improve the signal to noise ratio. High resolution 3D maps can be generated at 500–300 m altitude. Lower resolution 3D maps can be generated for altitudes up to 1000 m. With minor modifications the flash-LIDAR can also be used for other missions like in-orbit-servicing and for planetary rovers.

When iSpace’s Hakuto-R spacecraft crashed on the lunar surface, an early hypothesis emerged “One big rock.. could have negatively impacted the mission”. This highlights the risk of ‘blind’ landings based on available resolution Digital Elevation Models. This problem will only increase inline with the ambitious plans of ESA, NASA, and the CNSA for lunar exploration and exploitation. These involve increasingly hazardous landings around the irregular and rugged terrain of the south pole, where nobody has yet successfully performed a soft landing. MDA UK has developed a Lidar product line specifically designed around the needs of lunar landers: low power consumption because the power available during final descent is limited; high-speed long-range scans so that hazards can be detected far enough away to be avoided; dynamic scan correction so that the spacecraft does not need to hover and is able to perform corrective maneouvres mid-scan. Here we present testing and integration results.

In this paper we present the preliminary design of a FMCW based LiDAR for applications involving approaching large planetary bodies. To our knowledge this is the first of its kind allowing within a 25 × 25 degrees Field of View a maximum measurement range beyond 1 km and a point accuracy of 5.8 mm (at 500 m). The paper focuses on the performances of our approach and details the advantages in space of a FMCW system.

The application field of LIDARs is promising, and the technological advances are creating new opportunities in space. This introduces a need for flexible, power efficient and accurate time measurement solutions. At the same time, in the field of earth observation in particular, there is a push to a better viewing granularity for 2-D and 3-D areas, hence smaller pixels and higher data rates, while power consumption and weight of the solution remain critical. Magics Technologies has recently developed an ITAR-free time-to-digital converter chip with 8 ps single-shot precision, in cooperation with ESA, for extreme precision time measurements in space applications, like LIDAR and time tagging. The TDC is rad-hard-by-design and supports zero-dead-zone measurements in the range from 0 ps to 3 s. It also supports a multi-stop mode for capturing up to 5 consecutive STOP pulses. The chip has been validated for its electrical and radiation performance, and it is foreseen to get first flight heritage in 2024.

LIDAR technology plays a pivotal role in numerous space applications, including remote sensing, rendezvous and docking, debris detection and planetary landers. Existing spaceborne LIDAR technology employs discrete optical and optoelectronic components, resulting in relatively bulky designs with high power consumption. However, the continued developments in CubeSats and upcoming lander missions are leading to more demanding SWaP (size, weight and power) requirements. In order to meet the need for more compact designs, consideration is now being given to the application of photonic integrated circuits (PICs). This paper presents the preliminary design of a photonic integrated circuit (PIC) frequency-modulated continuous-wave (FMCW) LiDAR system. The proposed system exploits a hybrid integration approach, combining indium phosphide (InP) and silicon nitride (Si3N4) chips, to take advantage of their respective benefits.

Developing space-borne LIDAR for small satellite platforms requires miniaturization, ruggedization and high reliability of optoelectronic components. Lower size, weight and power (SWaP) LIDAR systems are achievable using monolithic photonic integrated circuit (PIC) platforms, hybrid photonic integration, and advanced photonic and electronic module packaging. Freedom Photonics’ monolithic InP PIC platforms, at wavelengths from 1250 to 1800+ nm, can integrate tunable lasers, amplifiers, modulators, detectors and more, in a chip with <1 cm2 footprint. Our photonic wirebonding capabilities enable integration of aura amplifiers, boosting output power to >1 W. High sensitivity avalanche photodetectors facilitate longer range detection, and high speed photodetectors can be used for offset locking. Additional capabilities are added by our InstaTune laser control module supporting wavelength stepping and stabilization within 200 ns. Proving in the reliability of these components, particularly transmitter PICs, high power amplifiers and photonic wirebonds, is currently a major effort at Freedom Photonics, with promising preliminary results.

In this paper, we present the two wind lidar architectures developed at ONERA: the heterodyne lidar which analyzes the backscattering of particles and the direct detection lidar using a QMZ which analyzes the backscattering of molecules. In both cases, solutions have been developed to be able to embark them on an airplane: fiber laser, robust receiver, robust general architecture. Both technologies could provide interesting comparative measurements for AEOLUS calibration/validation campaigns: the heterodyne configuration allows precise measurements on the lower part of the atmosphere while the QMZ configuration allows reaching up to at an altitude of 20 km. In addition, regarding the developments made for molecular lidar, the UV fiber laser and the monolithic QMZ receiver could be excellent solutions for the next generation of Aeolus to reduce costs, improve data quality and lidar durability.

ESA MObile RAman Lidar (EMORAL) was developed with the objective of participating in Cal/Val campaigns for ESA Earth Observation Programmes missions. Upgraded several times, current configuration and functionalities, especially broadband fluorescence and water vapor measurements together with wavelength-dependent polarization, backscattering and extinction coefficients observations, place EMORAL in the forefront of the modern lidar developments. Highly desirable state-of-art ensemble of near-real-time observations was collected in different areas (urban, industrial, rural, peatland, mountains, flatland), thus providing exclusive sets of quality-assured high-level data products. Implementation Quality Assurance tools and Single Calculus Chain data evaluation schemes of Aerosol Clouds and Trace Gases Research Infrastructure (ACTRIS) contributes to lidar smooth operation and derivation of high-quality, ACTRIS approved data. Moreover, EMORAL effectiveness to obtain new data products such as fluorescence backscatter coefficient and fluorescence capacity in demanding environments is demonstrated, e.g. within polluted city of Wrocław, Poland, suburban biomass-burning affected Măgurele, Romania, background urban outskirts of Vilnius, Lithuania, as well as extremely clean coastal Orašac, Croatia. The knowledge gained from operating the lidar in different conditions and identified recommendations will drive further advancements and ensure its continued successful operation in future campaigns.

HiLASE is participating in project LUGO for Moon geology study and a new concept of a SWIR laser for space communication. For LUGO we are developing a high energy short pulse fiber laser based on double clad fiber technology operating at 1.5 um for LiDAR for Moon surface profiling. Energies above 50 uJ for 1 ns long pulses at repetition rate of 50 kHz are expected. A similar laser concept can be used for Doppler LiDAR as well. For study of space communications in a new spectral band we are developing CW thin-disk laser operating close to 2.1 um to take benefit of spectral atmospheric window. An average power of 5 W is expected. Pulsed operation of such laser can be used for high energy LiDAR applications with pulse energies above 2 mJ at 1 kHz repetition rate.

In this work the integration of a microchip laser for space altimetry is presented. The use of microchip lasers allows for more efficient and compact Lidars. This is because these are solid state laser diode pumped lasers, with optical cavities in the millimetres. These characteristics are of paramount importance for space applications, where resources are limited. The development of the microchip laser involves the study of the configuration of its optical cavity. Erbium ions in the gain medium allows the emission of 1535 nm, which is considered eye safe. The setting of the input and output couplers determine the length of the optical cavity, which has an influence on the emitted pulse width. The addition of a saturable absorber allows for short high energy pulses.

We report on a novel expanded-beam fibre-optic contact and connector system that relies on active optical alignment and laser-welded construction, leading to optical losses consistently in the range of 0.25–0.5 dB over the temperature range of −40 to + 85 °C, tested up to power levels of 20 W. The contacts can support both standard single-mode and multi-mode circular core fibers as well as polarization-maintaining fibers. The optical contacts fit into a standard Size 8 connector cavity and can be fielded in D38999, D-sub or other styles of connector shell systems. Hybrid arrangements of optical contacts and electrical contacts are easily accommodated, allowing for make/break eye-safety interlocks to be easily supported. In this paper, we will report on the optical design considerations leading to these extremely low optical losses, as well as present test data for insertion loss over temperature, as well as vibration and shock.

The assembly stage plays a major role in the manufacturing chain of optical systems, as it can influence both the operational and non-operational performance of the whole system. When selecting a technology to build optical systems, various considerations arise, such as temperature and lifetime stability, radiation resistance (in the case of space applications), stress compensation, and outgassing, which with many others have a huge impact on the requirements for the final product. In order to fulfill the requirements of thermal and mechanical testing for space applications, while preserving its optical performance with the application of a laser beam solder technique (Solderjet bumping), a study on the design and selection of optical and mount materials with different sizes has been done, achieving promising results for the further application in space optics.

A high-speed Flash-LiDAR CMOS image sensor which is named FLAMES for landing missions is presented. The sensor features 1280(H) × 1024(V) array size with a pixel pitch of 14 µm. It offers a full-frame capture rate of 500 fps, up to 2000 fps for smaller ROI, such as 500(H) × 500(V). The sensor can operate in 3 different modes, and its time gating sharpness is anticipated to be faster than 5 ns. When correlated double sampling (CDS) is utilized, the readout noise is expected to be less than 10 e-. This paper discusses the architecture of FLAMES sensor, the design considerations employed to achieve high speed and fast time gating and presents relevant simulation results.

Eventech has demonstrated high competence in event timing, producing time-tagging systems with 2.5 ps precision used in more than half of the SLR stations in the world. Recently, we have implemented specific updates for the ET33 event timer, which allowed us to implement 25 Mevents/sec registration speed, 2 ps precision, and stabilize the performance of the ESTT in the operating temperature range. The internal time scale of the meter has high-precision synchronization with an external time scale (for example, with the UTC scale based on GPS signals). ESA has accepted our technology for space application; the closest mission is the 2024 HERA asteroid mission. It includes a centimeter-resolution PALT planetary altimeter, the main electronic unit of which is a 10 ps precise time interval meter for deep space applications. The active development phase for this project is completed now, and it is passing pre-flight tests.

The Atmospheric Dynamics Mission ADM-Aeolus was successfully launched in August 2018 by the European Space Agency (ESA). ADM-Aeolus carries the Atmospheric LAser Doppler INstrument (ALADIN), the first space-borne Doppler Wind Lidar (DWL) that provides vertical profiles of horizontal line-of-sight (HLOS) winds on a global scale. Aeolus satellite overpasses Cruzeiro do Sul (7.35 S, 72.46 W) twice a week in two different orbits, the descending orbit at 10:42 UTC on Tuesdays and the ascending orbit at 23:04 UTC on Sundays. In this study, we focus on the descending orbit overpasses, and statistical validation of Aeolus L2B wind products has been performed with radiosondes launched daily at 12:00 UTC. The period from October 2018 to March 2023, including Aeolus baselines 2B11, 2B12, 2B13, 2B14, and 2B15, was analyzed, and Pearson correlation coefficients greater than 0.7 (0.8) were observed in Rayleigh-clear (Mie-cloudy) wind products.

Several case studies of cirrus clouds are presented to highlight the advantages of the synergetic use of lidar and radar remote sensing for their characterization in terms of the ice water content (IWC) and particle effective radius (Reff), which are key cloud-relevant parameters in climatic models. They are derived from both lidar and radar observations carried out aboard current space-based platforms, e.g. CALIPSO and CloudSat. This preliminary work can represent an insight for the upcoming ESA EarthCARE mission.

The scientific goals of the MiLi project (‘Miniaturized Lidar for MARS Advanced Atmospheric Research’) are addressed to the characterization of Martian aerosols (dust and ice clouds) in vertical resolution. These studies will represent a key factor to investigate their climatic implications on Mars. First, a terrestrial version of the MiLi system is designed to be an elastic lidar with a [2β + 1δ] configuration, which represents an extended performance of the first lidar on Mars, the Phoenix mission, by incorporating, in particular, depolarization capabilities. Hence, the primary scientific MiLi challenges for Mars atmospheric exploration are three-fold: (1) detection of high-altitude dust and ice cloud layers (>30 km height; plausible dust-cloud interactions); (2) for the first time, estimation of their depolarization ratio; and (3) discrimination between dust and ice clouds. Earth-based representative atmospheric scenarios are simulated by considering different optical and microphysical properties of dust and ice cloud particles on Mars, being discussed in terms of expected lidar signal levels.

Cloud radiative forcing has a crucial role in current climate change. However, cloud-aerosol interaction on the Earth’s radiative balance is still poorly understood. Hence, a long-term database of ground-based and satellite cloud radar is crucial to further develop large scale cloud physics analysis. Additionally, ground-based radars are important to support current space missions such as EarthCARE, which is equipped with a 94 GHz cloud profiling radar (CPR). Thus, the cloud radar NEPHELE, operated at the ACTRIS/CLOUDNET Granada station (Spain) since 2018 with similar technical characteristics can be used for the calibration and validation (cal/val) of the CPR. NEPHELE provides reflectivity, spectral width and Doppler velocity with scanning capability at different angles, which can be used for EarthCARE CPR cal/val activities. Therefore, this work aims to show the radar capabilities for the cal/val activities to be developed at Granada.

A multi-year Cal/Val comparison of the Aeolus satellite mission's L2A, L2B, and L2C products with ground-based aerosol and Doppler lidars was carried out at the Granada-ACTRIS site in Spain. The aim of this study is to assess the accuracy and quality of Aeolus aerosol and wind products from July 2019 to July 2022, enabling a robust evaluation of Aeolus performance under multiple atmospheric conditions. Results indicate a good but limited agreement between Aeolus products, ground-based lidars and radiosondes, endorsing the satellite's capability to provide valuable aerosol and wind products. Substantial discrepancies were observed primarily at lower altitudes (below 1 km agl) due to larger spatial inhomogeneities and lower signal-to-noise ratio.

We present new parametric source architectures for future spaceborne Differential Absorption Lidar (DIAL). This work focalizes on the developments performed during LEMON H2020 project using periodically poled nonlinear crystals. Such phase matching configuration offers the possibility to go towards more simple and robust set-ups for future space operation. We investigated injection-free optical parametric oscillator OPO set-ups, such as the Nested Cavity OPO–which allows a broad tuning range and thus can address several gas species with a single OPO—and also propose an injection and cavity free OPO solution using the counter-propagating phase matching configuration (Backward wave OPO). Moreover, we studied the implementation of high efficiency optical parametric amplifiers, to investigate the possibility to scale the output energies to several tens of mJ in the 2 µm region, and performed radiation testing on the specifically developed, large aperture, periodically poled KTP crystals.

Space mission like Aeolus has demonstrated how much LiDAR instruments can bring to the quality of the data gathered and therefore analysis and prediction that scientist can make. The design of a LiDAR detector comes with challenges. The main and most difficult performance to reach is the signal-to-noise ratio due to the weak level of the signal reflected. It requires a detector of the highest sensitivity. This paper will present the LiDAR detector used for Aeolus, the technologies developed to increase the sensitivity of such detector and finally more recent development of indirect Time-Of-Flight (iToF) at Teledyne-e2v.