The EarthCARE satellite: the next step forward in global measurements of clouds, aerosols, precipitation, and radiation

The collective representation within global models of aerosol, cloud, precipitation, and their radiative properties remains unsatisfactory. They constitute the largest source of uncertainty in predictions of climatic change and hamper the ability of numerical weather prediction models to forecast high-impact weather events. The joint European Space Agency (ESA)–Japan Aerospace Exploration Agency (JAXA) Earth Clouds, Aerosol and Radiation Explorer (EarthCARE) satellite mission, scheduled for launch in 2018, will help to resolve these weaknesses by providing global profiles of cloud, aerosol, precipitation, and associated radiative properties inferred from a combination of measurements made by its collocated active and passive sensors. EarthCARE will improve our understanding of cloud and aerosol processes by extending the invaluable dataset acquired by the A-Train satellites CloudSat, Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and Aqua. Specifically, EarthCARE’s cloud profiling radar, with 7 dB more sensitivity than CloudSat, will detect more thin clouds and its Doppler capability will provide novel information on convection, precipitating ice particle, and raindrop fall speeds. EarthCARE’s 355-nm high-spectral-resolution lidar will measure directly and accurately cloud and aerosol extinction and optical depth. Combining this with backscatter and polarization information should lead to an unprecedented ability to identify aerosol type. The multispectral imager will provide a context for, and the ability to construct, the cloud and aerosol distribution in 3D domains around the narrow 2D retrieved cross section. The consistency of the retrievals will be assessed to within a target of ±10 W m–2 on the (10 km)2 scale by comparing the multiview broadband radiometer observations to the top-of-atmosphere fluxes estimated by 3D radiative transfer models acting on retrieved 3D domains

A novel satellite mission concept for upper air water vapour, aerosol and cloud observations using integrated path differential absorption LiDAR limb sounding

We propose a new satellite mission to deliver high quality measurements of upper air water vapour. The concept centres around a LiDAR in limb sounding by occultation geometry, designed to operate as a very long path system for differential absorption measurements. We present a preliminary performance analysis with a system sized to send 75 mJ pulses at 25 Hz at four wavelengths close to 935 nm, to up to 5 microsatellites in a counter-rotating orbit, carrying retroreflectors characterized by a reflected beam divergence of roughly twice the emitted laser beam divergence of 15 µrad. This provides water vapour profiles with a vertical sampling of 110 m; preliminary calculations suggest that the system could detect concentrations of less than 5 ppm. A secondary payload of a fairly conventional medium resolution multispectral radiometer allows wide-swath cloud and aerosol imaging. The total weight and power of the system are estimated at 3 tons and 2,700 W respectively. This novel concept presents significant challenges, including the performance of the lasers in space, the tracking between the main spacecraft and the retroreflectors, the refractive effects of turbulence, and the design of the telescopes to achieve a high signal-to-noise ratio for the high precision measurements. The mission concept was conceived at the Alpbach Summer School 2010

Characterization of clouds and their radiative effects using ground-based instrumentation at a low-mountain site

The interaction of clouds with radiation and aerosols is the greatest source of uncertainty in future climate projections. Part of the reason is the limited amount of observations of clouds and hence the limited knowledge of cloud macro- and microphysical statistics in connection to their effects on the radiative budget and on the vertical redistribution of energy within the atmosphere. In 2007, the Atmospheric Radiation Measurement program�s (ARM) Mobile Facility (AMF) was operated for a nine-month period in the Murg Valley, Black Forest, Germany, in support of the Convective and Orographically-induced Precipitation Study (COPS). Based on the measurements of the AMF and COPS partner instrumentation, the present study aims at improving the data basis of cloud macro- and microphysical statistics and to assess the potential of the derived cloud properties to estimate the radiative effects of clouds. The synergy of various instruments is exploited to derive a data set of high quality thermodynamic and cloud property profiles with a temporal resolution of 30 s. While quality filters in the cloud microphysical retrieval techniques mostly affect the representativity of ice and mixed clouds in the data sample, water clouds are very well represented in the derived 364,850 atmospheric profiles. In total, clouds are present 72% of the time with multi-layer mixed phase (28.4%) and single-layer water clouds (11.3%) occurring most frequently. In order to evaluate the derived thermodynamic and cloud property profiles,radiative closure studies are performed with independent radiation measurements. In clear sky, average differences between calculated and observed surface fluxes are less than 2.1% and 3.6% for the shortwave and longwave, respectively. In cloudy situations, differences, in particular in the shortwave, are much larger, but most of these can be related to broken cloud situations. The cloud radiative effect (CRE), i.e. the difference of cloudy and clear-sky net fluxes, has been analyzed for the whole nine-month period. The largest surface (SFC) net CRE has been found for multi-layer water (-110 Wm-2) and mixed clouds (-116 Wm-2). The estimated uncertainties in the modeled SFC and top of atmopshere (TOA) net CRE are up to 39% and 26%, respectively. For overcast, single-layer water clouds, sensitivity studies reveal that the SW CRE uncertainty at the SFC and TOA is likewise determined by uncertainties in liquid water path (LWP) and effective radius, if the LWP is larger than 100 gm-2. For low LWP values, uncertainties in SFC and TOA shortwave CRE are dominated by the uncertainty in LWP. Uncertainties in CRE due to uncertainties in the shape of the liquid water content (LWC) profile are typically smaller by a factor of two compared to LWP uncertainties. For the difference between the cloudy and clear-sky net heating rates, i.e. the cloud radiative forcing (CRF), of water clouds, the LWP and its vertical distribution within the cloud boundaries are the most important factors. In order to increase the accuracy of LWC profiles and consequentially of the estimates of CRE and CRF, advanced LWC retrieval techniques, such as the Integrated Profiling Technique (IPT), are needed. The accuracy of a LWC profile retrieval using typical microwave radiometer brightness temperatures and/or cloud radar reflectivities is investigated for two realistic cloud profiles. The interplay of the errors of the a priori profile, measurements and forward model on the retrieved LWC error and on the information content of the measurements is analyzed in detail. It is shown that the inclusion of the microwave radiometer observations in the LWC retrieval increases the number of degrees of freedom, i.e. the independent pieces of information in the measurements, by about 1 compared to a retrieval using measuremets from the cloud radar alone. Assuming realistic measurement and forward model errors, it is further demonstrated, that the error in the retrieved LWC is 60% or larger, if no a priori information is available, and that a priori information is essential for a better accuracy. The results of the present work strongly suggest to improve the LWC a priori profile and the corresponding error estimates in the IPT. However, there are few observational datasets available to construct accurate a priori profiles of LWC, and thus more observational data are needed to improve the knowledge of the a priori profile and the corresponding error covariance matrix

Lidar remote sensing and co-operative observations: Processing methods and aerosol radiative transfer

This Ph.D. thesis focuses on: (i) the design and integration of a polarimetric channel for the multi-spectral Raman lidar station of the Universitat Politècnica de Catalunya (UPC), Remote Sensing, Antennas, Microwaves and Superconductivity Group (CommSensLab), (ii) the study of the temporal and spatial evolution of atmospheric aerosol optical, microphysical and radiative properties by means of active and passive remote sensing in the context of ACTRIS and Spanish National projects, and (iii) rainfall rate retrieval by means of a vertically-pointed ceilometer in the context of the Verification of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE). The first goal of this Ph.D., tested on the UPC multi-spectral Raman lidar station, consists of developing a secondary optical receiving chain, installed next to the laser source. The secondary telescope, mounted in the optical chain, allows retrieving the cross-polarized return signal separately from the total-power signal, avoiding the need of a very precise characterization of the crosstalk parameters of the beam-splitters. The first experimental results, corresponding to a collection of atmospheric conditions over the city of Barcelona, are also presented. The second goal of this Ph.D. deals first with the GAME (Global Atmospheric Model) code, necessary to retrieve the aerosol radiative properties. The radiative fluxes estimated in the short-wave and long-wave spectral ranges at the bottom and the top of the atmosphere by GAME are compared to the ones retrieved by a different radiative transfer model, namely Two-Stream, in order to know the importance of the spectral parameterization of a radiative transfer code. Then, GAME code, in both configurations, is fed by means of three different datasets to evaluate the parameterization of the vertically-resolved properties and to assess the uncertainty of GAME when is tuned with input parameters from different sources. Afterwards, an evaluation of the seasonal variability of the aerosol background optical and radiative properties in the Western Mediterranean Basin (WMB) is performed by means of AERONET (Aerosol Robotic Network) sun-photometers data from two background sites, Ersa (Corsica Island, France) and Palma de Mallorca (Mallorca Island, Spain). In addition, in order to detect possible northeast-southwest gradients in the aerosol properties, a third site located at Abolrán (Alborán Island, Spain) is considered. Finally, during 15-24 June 2013 a moderate Saharan dust multi-intrusion was detected by some EARLINET/ACTRIS (Granada, Barcelona, Naples, Potenza and Serra la Nave (Italy)) and ADRIMED/ChArMEx (Cap d’en Font, (Minorca Island, Spain) and Ersa) stations. This Ph.D. uses this event to study the spatio-temporal evolution of the mineral dust properties, since the lidar stations were supported during the multi-intrusion by collocated AERONET sun-photometers and the Falcon 20 aircraft. Also the GAME code is used to estimate the aerosol radiaite effect during the Saharan dust event. Besides, air- and space-borne lidar measurements, satellite images and back-trajectories are used to confirm the multi-intrusion aspect of the event. The last goal of this Ph.D. pursues estimation of the rain rate (RR) from ceilometer measurements. In VORTEX-SE, a Vaisala CL-31 ceilometer, a S-band radar, and a disdrometer were deployed in Alabama during March-April 2016. First, rain-extinction coefficients from ceilometer attenuated backscatter measurements are derived by means of a modified form of the well-known slope-method. These coefficients are compared with the RRs measured by a collocated S-band radar and a disdrometer in order to get the RR-to-extinction models. Advanced covariance-weighted techniques are used to best assess and validate the estimated models. These models can be used to estimate the RR from the ceilometer in similar situations without need to have a collocated cooperative instrument permanently deployed.Este Ph.D. se centra en: (i) en el diseño e integración de un canal polarimétrico para la estación lidar multi espectral del grupo de teledetección, antenas, microondas y superconductividad (CommSensLab) de la Universitat Politècnica de Catalunya (UPC), (ii) en el estudio de la evolución temporal y espacial de las propiedades ópticas, microfísicas y radiativas de los aerosoles por medio de teledetección activa y pasiva en el contexto de ACTRIS y proyectos estatales, y (iii) en la recuperación de intensidad de lluvia por medio de un ceilómetro en configuración vertical en el contexto del proyecto Verification of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE). El primer objetivo, realizado en la estación lidar de UPC, consiste en el desarrollo de una cadena óptica secundaria instalada junto al láser. El telescopio secundario, montado en la cadena óptica, permite recuperar la componente cross-polarized de la señal total por separado, evitando la necesidad de conocer con precisión los parámetros de los beam-splitters. Se presentan también los primeros resultados obtenidos en Barcelona durante diferentes situaciones atmosféricas. El segundo objetivo de este Ph.D. se centra en el código GAME (Global Atmospheric Model), necesario para recuperar las propiedades radiativas de los aerosoles. Los flujos radiativos estimados tanto en onda larga como en onda corta en la base y en la parte superior de la atmósfera son comparados con los estimados por otro código de transferencia radiativa, Two-Stream, para conocer la importancia de la parametrización espectral. Después, el código GAME es alimentado con 3 bases de datos diferentes para evaluar la parametrización de las propiedades resueltas en altura y conocer la incertidumbre de GAME cuando es alimentado con parámetros con diferentes orígenes. Por otro lado, se presenta una evaluación de la variabilidad estacional de las propiedades ópticas y radiativas del aerosol de fondo en la cuenca oeste mediterránea (WMB) realizada con datos de fotómetros solares de la red AERONET (Aerosol Robotic Network) situados en dos puntos considerados libres de contaminación: Ersa (isla de Córcega, Francia) y Palma de Mallorca. Además, para detectar posibles gradientes noreste-suroeste en las propiedades delos aerosoles, se considera un tercer punto ubicado en la isla de Alborán. Por último, en este Ph.D. se aprovecha una multi intrusión moderada de polvo sahariano, detectada entre los días 15 y 24 de junio de 2013 por algunas estaciones EARLINET/ACTRIS (Granada, Barcelona, Nápoles, Potenza y Serra la Nave (Italia)) y ADRIMED/ChArMEx (Cap d'en Font (Menorca) y Ersa), para estudiar la evolución espacio-temporal de las propiedades del polvo mineral, ya que las estaciones lidar estaban apoyadas durante el evento por fotómetros solares pertenecientes a la red AERONET, situados junto a las estaciones lidar, y por vuelos del Falcon 20. GAME es usado para obtener también el efecto radiativo de los aerosoles durante el evento de polvo sahariano. Para confirmar el aspecto de multi intrusión se utilizan medidas lidar tomadas a bordo de aviones y satélites, imágenes satelitales y retro trayectorias. El último objetivo del Ph.D. persigue la estimación de la RR utilizando medidas de un ceilómetro. En VORTEX-SE, se desplegaron (Alabama, marzo-abril 2016) un ceilómetro Vaisala CL-31, un radar de banda S y un disdrómetro. Se han estimado los coeficientes de extinción debida a la lluvia a partir del retorno atenuado medido por el ceilómetro, utilizando una versión modificada del método de la pendiente. Estos coeficientes se comparan con las intensidades de lluvia (RR) estimadas con el radar y el disdrómetro para obtener modelos de RR-extinción. Para validarlos se utilizan técnicas avanzadas de covarianza ponderada. Dichos modelos pueden usarse para estimar la RR con un ceilómetro, en situaciones similares, sin necesidad de tener desplegado permanentemente un instrumento cooperativo.Postprint (published version

Radio-wave communication with chaos

This research is supported in part by National Natural Science Foundation of China (61172070), Scientific and Technological Innovation Leading Talents Program of Shaanxi Province, The Key Basic Research Fund of Shaanxi Province (2016ZDJC-01).Peer reviewedPublisher PD

Design of a flexible and low-power ionospheric sounder

Thesis (M.S.) University of Alaska Fairbanks, 2014Characterizing the structure of the ionosphere has practical applications for telecommunications and scientific applications for studies of the near-earth space environment. Among several methods for measuring parameters of the ionosphere is ionospheric sounding, a radar technique that determines the electron content of the ionosphere as a function of height. Various research, military, and commercial institutions operate hundreds of ground-based ionosondes throughout the globe, and new ionosondes continue to be deployed in increasingly remote and distant locations. This thesis presents the design of an ionospheric sounder that reduces the power, size, and cost compared to existing systems. Key improvements include the use of an open-source software-defined radio platform and channel-aware dynamic sounding scheduling.Chapter 1. Introduction -- 1.1. A brief historical background -- 1.2. The ionosphere -- 1.3. Instruments for studying the ionosphere -- 1.4. Thesis organization -- Chapter 2. Radio waves and the ionosphere -- 2.1. Dispersion relation of electromagnetic waves in the ionosphere -- 2.2. Power reflected from the ionosphere -- 2.3 Noise in the HF spectrum -- 2.4. Ionograms -- Chapter 3. Radar principles -- 3.1. Target detection -- 3.2. Range and doppler elocity -- 3.3. Range-doppler ambiguity -- 3.4. Resolution and precision --3.5. Multi-pulse integration -- 3.6. Pulse compression -- 3.7. Practical limits of performance -- Chapter 4. Survey of current systems -- 4.1. Coherent transmission/reception and digital systems -- 4.2. Phase-coded pulses -- 4.3. Coherent integration of multiple pulses -- 4.4. Phased antenna arrays -- 4.5. O- and X-mode discrimination -- Chapter 5. System description -- 5.1. Design approach -- 5.2. Overview of the Ettus Research USRP -- 5.3. Using the USRP as a radar -- 5.4. Waveform Generation -- 5.5. Processing the received signal -- 5.6. Scheduling -- 5.7. Completing the system -- Chapter 6. Sounding results -- 6.1. Single frequency soundings -- 6.2. Swept frequency soundings -- Chapter 7. Conclusion -- 7.1. Evaluation of performance -- 7.2. Costs -- 7.3. Future improvements -- 7.4. Deploying a terrestrial ionosonde -- 7.5. Deploying a space-borne ionosonde -- References

Remote Sensing of Heat Fluxes Validation and Inter-Sensor Comparison

Instantaneous heat fluxes were modeled using data obtained from Landsat 5 TM (Thematic Mapper), Landsat 7 ETM+ (Enhanced Thematic Mapper Plus) and Terra MODIS (Moderate Resolution Imaging Spectroradioineter) using the Surface Energy Balance Algorithm for Land (SEBAL) model for cloud-free days. The modeled results were compared with measurements of net radiation (both incoming and outgoing, shortwave and longwave), soil sensible and latent heat fluxes from two flux towers located in Brookings, SD, and Fort Peck, MT. Flux tower data consisted of 30 minute averages at every half an hour, and footprints of contributing movement of air within the period were estimated for each satellite overpass by taking into account the factors of observation height, atmospheric stability, and surface roughness, as well as wind speed and directions (Hsieh et al. 2000). It was found that footprints (considering 90% contributing areas) were normally larger than the size of one Landsat pixel (30 m) but smaller than that of one MODIS pixel (1 km). Therefore, for Landsat the data were averaged for pixels within the concurrent footprint, and for MODIS the data for the particular pixel covering the flux tower was used. The R values between the modeled and the observed net radiation (Rn) for Landsat and MODIS were found to be 0.70 and 0.66, respectively. Relatively, comparisons between modeled and observed values were better at Brookings than at Fort Peck for both sensors. This may be because the former site has a relatively flat topography and larger fetch than the latter, minimizing the possible effects of terrain heterogeneity on incoming and outgoing radiation modeling. Both satellites performed poorly in modeling soil heat flux (G0) . Our results show that SEBAL provides a better modeling of sensible heat flux (H) with Landsat (R2= 0.62) than with MODIS (R2 = 0.11), even though the MODIS performance for estimating latent heat flux (lambdaE) improved (R2 = 0.37). The improvement found in estimating latent heat flux is probably due to the fact that in SEBAL cold pixels are used to estimate air temperature and then also used in computation for both Rn and H. The uncertainties associated with this assumption cancelled out in deriving lambdaE. Overall, SEBAL performed better in modeling the heat fluxes when Landsat data were used. This may be due to the scaling issue, as the footprint areas were always significantly less than a single MODIS pixel. By simulating MODIS observations using Landsat, it was found that the R2 value for the aggregated Landsat pixels decreased from 0.62 to 0.25 with an increase of root mean square difference (RMSD) from 50.5 to 68.3 Wm\u272. This suggested that the poor performance of MODIS in estimating heat fluxes was due to heterogeneity of the surface within a field of view. In addition, sensitivity analyses of the model to input parameters suggested that the model is more sensitive to surface-to- air temperature difference than to surface roughness conditions. Appendix A lists symbols mentioned in this thesis

THE DIURNAL AND SEASONAL RADIATIVE EFFECTS OF CIRRUS CLOUDS UTILIZING LARGE AIRBORNE AND SPACE-BORNE LIDAR DATASETS

Cirrus clouds are globally the most common cloud type, however, their radiative impact on the Earth remains a large source of uncertainty in global climate models. Cirrus are unique in that they are absorptive to terrestrial outgoing longwave radiation, while also relatively transmissive to incoming solar radiation. The interactions of this greenhouse and albedo effect determine the sign and magnitude of cirrus radiative effects. Cirrus are microphysically complex, and can exhibit a variety of different ice crystal shapes and sizes depending on the thermodynamic environment in which they form, and their dynamic formation mechanism. Our ability to reliably model cirrus radiative effects is dependent upon accurate observations and parameterizations incorporated into radiative transfer simulations. Laser lidar instruments provide valuable measurements of cirrus clouds unavailable by other radar systems, passive remote sensors, or in-situ instruments alone. In this dissertation I developed and tested an improved calibration technique for the ACATS lidar instrument, and its impact on the direct retrieval of cirrus HSRL optical properties. HSRL retrievals theoretically have reduced uncertainty over those from a standard backscatter lidar. ACATS flew on two field campaigns in 2012 and 2015 where it was unable to consistently calibrate its etalon. It has been operating from the lab in NASA GSFC collecting zenith pointing data of cirrus layers where the improved calibration has resulted in consistent and reliable separation of the particulate and Rayleigh signal components. The diurnal trend of cirrus influence on the global scale has primarily been limited to data provided by satellites in sun-synchronous orbit, which provide only a snapshot of conditions at two times a day. Utilizing data from the CATS lidar aboard the ISS I investigated cirrus at four periods throughout the day in morning, afternoon, evening, and night across all seasons. Cirrus radiative effects were found to have a large latitudinal dependence, and have a greater potential to cool than many studies suggest with their primary warming contributions skewed towards the nighttime hours. Constrained lidar retrievals reduce the assumptions made in retrieving cirrus optical properties. Utilizing the expansive airborne CPL dataset from six flight campaigns I model the radiative effects of over twenty thousand constrained cirrus observations. Mid-latitude cirrus were found to have a mean positive daytime forcing equivalent to that of the CO2 greenhouse effect. However, synoptic cirrus were found to have a greater warming effect than convective cirrus, which were more likely to have a cooling effect