Lidar In-space Technology Experiment Research Articles

Characteristics of CALIPSO and CloudSat Backscatter at the Top Center Layers of Mesoscale Convective Systems and Relation to Cloud Microphysics

Abstract Following the discovery of anomalously high values of lidar integrated attenuated backscatter near the top center layers of mesoscale convective systems (MCSs) observed by the NASA Lidar In-Space Technology Experiment (LITE), a search of Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) data on board the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) platform revealed the same phenomena in a sample of eight MCSs investigated. The backscatter depolarization ratio also showed changes concurrent with the high integrated backscatter and either increased or decreased concurrently with the anomalous backscatter. Simultaneous CloudSat data in the A-Train formation showed a cloud-top altitude similar to that measured by CALIOP, indicating fairly large ice crystals were reaching cloud top. Based on previous work, the CALIOP and CloudSat returns were likely due to a mix of small ice droxtals or frozen drops extending in a continuous spectrum to large crystals composed of well-formed hexagonal columns, thick hexagonal plates, spheroids, and irregular particles. The CALIOP lidar would detect the whole spectrum whereas CloudSat would detect ice crystals greater than ∼30 μm in effective radius; there were apparently enough of such crystals to allow CloudSat to detect a cloud-top height similar to that found by CALIOP. Using such a model, it was estimated that the measured backscatter phase function in the most active part of the cloud could be reconciled approximately with theoretical values of the various crystal habits. However, it was harder to reconcile the changes in depolarization ratio given the absence of values of this parameter for small droxtal crystals.

The Retrieval of Profiles of Particulate Extinction from Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) Data: Algorithm Description

Abstract This work describes the algorithms used for the fully automated retrieval of profiles of particulate extinction coefficients from the attenuated backscatter data acquired by the lidar on board the Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) spacecraft. The close interaction of the Hybrid Extinction Retrieval Algorithms (HERA) with the preceding processes that detect and classify atmospheric features (i.e., cloud and aerosol layers) is described within the context of the analysis of measurements from scenes of varying complexity. Two main components compose HERA: a top-level algorithm that selects the analysis pathway, the order of processing, and the analysis parameters, depending on the nature and spatial extent of the atmospheric features to be processed; and a profile solver or “extinction engine,” whose task it is to retrieve profiles of particulate extinction and backscatter coefficients from specified sections of an atmospheric scene defined by the top-level algorithm. The operation of these components is described using synthetic data derived from Lidar In Space Technology Experiment (LITE) measurements. The performance of the algorithms is illustrated using CALIPSO measurements acquired during the mission on 1 January 2007.

Comparison of cloud statistics from spaceborne lidar systems

Abstract. The distribution of clouds in a vertical column is assessed on the global scale through analysis of lidar measurements obtained from three spaceborne lidar systems: LITE (Lidar In-space Technology Experiment, NASA), GLAS (Geoscience Laser Altimeter System, NASA), and CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization). Cloud top height (CTH) is obtained from the LITE profiles based on a simple algorithm that accounts for multilayer cloud structures. The resulting CTH results are compared to those obtained by the operational algorithms of the GLAS and CALIOP instruments. Based on our method, spaceborne lidar data are analyzed to establish statistics on the cloud top height. The resulting columnar results are used to investigate the inter-annual variability in the lidar cloud top heights. Statistical analyses are performed for a range of CTH (high, middle, low) and latitudes (polar, middle latitude and tropical). Probability density functions of CTH are developed. Comparisons of CTH developed from LITE, for 2 weeks of data in 1994, with ISCCP (International Satellite Cloud Climatology Project) cloud products show that the cloud fraction observed from spaceborne lidar is much higher than that from ISCCP. Another key result is that ISCCP products tend to underestimate the CTH of optically thin cirrus clouds. Significant differences are observed between LITE-derived cirrus CTH and both GLAS and CALIOP-derived cirrus CTH. Such a difference is due primarily to the lidar signal-to-noise ratio that is approximately a factor of 3 larger for the LITE system than for the other lidars. A statistical analysis for a full year of data highlights the influence of both the Inter-Tropical Convergence Zone and polar stratospheric clouds.

Multiple‐scattering lidar from both sides of the clouds: Addressing internal structure

Multiple‐scattering (a.k.a. “off‐beam”) lidar is an emerging technology in cloud remote sensing. It delivers, as in classic lidar ceilometry, cloud base altitude but also the cloud's physical thickness H as well as its optical depth τ (averaged over horizontal scales on the order of H). The value of τ in fact must lie beyond the range accessible by standard (i.e., single‐scattering/on‐beam) lidar profiling, namely, up to 3–4. A refined diffusion‐theoretical model is presented here for signals from multiple‐scattering lidar and applied, on the one hand, to retrieval algorithm development and, on the other hand, signal‐to‐noise ratio (SNR) estimation. SNRs are computed for LANL's ground‐based Wide‐Angle Imaging Lidar (WAIL) system and NASA's space‐based Lidar‐In‐space Technology Experiment (LITE). The refinements are threefold and all about internal structure. First, the laser source is modeled as a collimated anisotropic exponentially distributed internal source rather than an isotropic point source at the cloud boundary; this opens the possibility of using δ‐Eddington rescaling to capture the forward peaked phase function more effectively within the diffusion framework. Second, stratification of the scattering coefficient is modeled as an increasing function of distance to cloud base; this strongly differentiates the signals when observed from above or from below. Finally, Cairns' rescaling is applied to this conservative scattering problem to account for the systematic effects of random (turbulence‐driven) internal variability at scales up to a few mean free paths.

Desert dust aerosol columnar properties over ocean and continental Africa from Lidar in‐Space Technology Experiment (LITE) and Meteosat synergy

The new generation of spaceborne backscatter lidar systems, prefigured by the Lidar in‐Space Technology Experiment (LITE) mission in September 1994, will give new insight on the vertical distribution of both aerosols and clouds in the atmosphere. This is especially of importance for aerosols over land, where retrievals from passive sensors are known to be more difficult because of the surface contribution. Here we analyze mineral dust aerosol transport events through a new approach coupling the active LITE and passive Meteosat‐5 spaceborne observations. The Meteosat‐derived aerosol optical thickness at 550 nm is shown to be a good boundary condition for the lidar inversion in order to retrieve both the aerosol backscatter to extinction ratio (BER) and the aerosol extinction vertical profile above the Tropical Atlantic Ocean (TAO) and the Mediterranean Sea. Sensitivity tests indicate that the aerosol scattering coefficient is retrieved within a 20% relative uncertainty. Air mass trajectories allow us to further retrieve the vertical profile of aerosol optical properties over the continent in the Saharan Heat Low (SHL) region using the BER determined over the ocean. Results confirm a large dispersion of the BER which is not attributed to errors in the method. This shows the need to account for such dispersion in the retrieval of dust aerosol optical thickness and aerosol impact on the earth radiative budget. The coupling between LITE and Meteosat‐5 made here is shown to be interesting for an improvement of the direct dust aerosol forcing, and results should be improved by the CALIOP‐MODIS synergy.

Estimating random errors due to shot noise in backscatter lidar observations

We discuss the estimation of random errors due to shot noise in backscatter lidar observations that use either photomultiplier tube (PMT) or avalanche photodiode (APD) detectors. The statistical characteristics of photodetection are reviewed, and photon count distributions of solar background signals and laser backscatter signals are examined using airborne lidar observations at 532 nm using a photon-counting mode APD. Both distributions appear to be Poisson, indicating that the arrival at the photodetector of photons for these signals is a Poisson stochastic process. For Poisson- distributed signals, a proportional, one-to-one relationship is known to exist between the mean of a distribution and its variance. Although the multiplied photocurrent no longer follows a strict Poisson distribution in analog-mode APD and PMT detectors, the proportionality still exists between the mean and the variance of the multiplied photocurrent. We make use of this relationship by introducing the noise scale factor (NSF), which quantifies the constant of proportionality that exists between the root mean square of the random noise in a measurement and the square root of the mean signal. Using the NSF to estimate random errors in lidar measurements due to shot noise provides a significant advantage over the conventional error estimation techniques, in that with the NSF, uncertainties can be reliably calculated from or for a single data sample. Methods for evaluating the NSF are presented. Algorithms to compute the NSF are developed for the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations lidar and tested using data from the Lidar In-space Technology Experiment.

Cloud heights from TOVS Path‐B: Evaluation using LITE observations and distributions of highest cloud layers

Cloud height from the TIROS‐N Operational Vertical Sounder (TOVS) Path‐B climate data set has been evaluated by using vertical profiles of the backscattered radiation at 532 nm from quasi‐simultaneous Lidar In‐space Technology Experiment (LITE) observations. Two averaging methods for the LITE inversion have been studied. Because of the LITE noise level and the difficulty in determining the vertical structure of thick clouds, we have chosen to apply the inversion on the average backscatter signal of the LITE spots over regions of 1° latitude × 1° longitude, which is also the spatial resolution of the TOVS Path‐B data set. The cloud height determined by TOVS corresponds well in general to the height of the “apparent middle” of the cloud system with coincidences for 53% of TOVS Path‐B low‐level clouds within 1 km and for 49% of TOVS Path‐B high‐level clouds within 1.5 km. In addition, 22.5% of TOVS Path‐B low‐level clouds are covered by a very thin high cloud layer not detectable by TOVS. Comparing for these cases the TOVS cloud height with the second LITE cloud layer increases the overall agreement for low‐level clouds to about 64%. High‐level clouds appear more often in multilayer systems (about 75%) and are also vertically more extended. Differences in average cloud height of high‐level clouds appear only to be significant (13.3 km from LITE compared to 11.3 km from TOVS Path‐B) in the tropics with a large extent of laminar cirrus situated near the tropopause. The height of maximum backscatter of most thick clouds is several hundred meters above “apparent cloud midlevel,” whereas thin high‐level clouds with underlying lower clouds provide a backscatter signal nearer to apparent cloud midlevel. In the latter case, the retrieved TOVS Path‐B cloud height is on average 280 m underestimated. Pressure distributions of the highest cloud layer weighted by effective cloud amount confirmed that high clouds have the lowest pressure in the tropics because of a higher tropopause, and in these regions there are nearly no cloud systems with the highest cloud layer in the middle troposphere. The Southern Hemisphere midlatitudes are mostly covered by low‐level clouds. Seasonal differences in the Northern Hemisphere (midlatitudes, with more equally distributed cloud altitudes in winter) are mostly caused by changes over land.

Simulation of the yield and accuracy of wind profile measurements from the Atmospheric Dynamics Mission (ADM-Aeolus)

The European Space Agency's ADM-Aeolus mission will for the first time provide wind profile measurements from space. In this study we carry out global simulations to predict the yield (i.e. quantity) and accuracy of future ADM-Aeolus wind profile measurements, using realistic clouds and climatological aerosol distributions. Based on an assessment of wind analysis accuracy, we argue that the main Aeolus impacts on global data assimilation are to be expected (i) in the jet streams over the oceans, especially away from main air traffic routes, and in the African/Asian subtropical jet, (ii) in the lower troposphere, e.g. western parts of the N. Pacific and N. Atlantic oceans, if cloud gaps are sufficient, and (iii) in the tropics, where mass–wind balance is weak and hence temperature information is not effective for inferring wind. These expectations are supported by the simulations of the yield and accuracy of ADM-Aeolus data. Observational data from the 1994 Lidar In-space Technology Experiment (LITE) are used to provide realistic profiles of cloud cover as input to such simulations. Profiles of model cloud cover are also used and these are validated against the LITE data. While the overall occurrence of model cloud agrees well with LITE-inferred cloud, model cloud cover underestimates the observations by around 20%. The use of model cloud cover for simulating Aeolus data thus results in a modest overestimation of Aeolus penetration altitude. Probability distributions of Aeolus instrument error show good agreement between simulations with observed and model cloud, but the worst 10% of errors are underestimated when model cloud cover is used. The mission-specified accuracy requirement for the free troposphere (instrument error below 2 m s−1) is met by more than 90% of the simulated data. The corresponding requirement for the boundary layer (instrument error below 1 m s−1) is met by two thirds of simulated data from the Mie channel, even when substantial cloud is encountered and under conservative assumptions about aerosol backscatter. It is shown that, after accounting for errors of representativeness, such data can be expected to receive appreciable weight in global data-assimilation systems. Copyright © 2005 Royal Meteorological Society

Mean radiative energy balance and vertical mass fluxes in the equatorial upper troposphere and lower stratosphere

We use radiative transfer calculations to quantify vertical mass transport in the equatorial upper troposphere (UT) and lower stratosphere (LS), employing high resolution sonde measurements of temperature, ozone and water vapor at seven equatorial locations (10°S–10°N). The influence of clouds is examined using data from the International Satellite Cloud Climatology Project (ISCCP) and the Lidar‐In‐Space Technology Experiment (LITE). The resulting mean heating rate profiles show that the transition from radiative cooling to heating occurs significantly lower in the full sky case than in the clear sky case, demonstrating the importance of clouds for processes in the UT, such as troposphere‐to‐stratosphere transport (TST). The heating rate profiles are used to calculate mean vertical mass fluxes, which show a divergent mass flux from 15–19 km. This suggests that only a small part of the air ascending through the cold point tropopause can reach the middle stratosphere. Above 19 km the vertical motion is a non‐divergent upwelling mass flux consistent with the idea of a Brewer‐Dobson circulation driven by waves dissipating in the extratropical stratosphere. Lower down, other processes are also responsible for the upwelling.

Use of probability distribution functions for discriminating between cloud and aerosol in lidar backscatter data

In this paper, we describe the algorithm that will be used during the upcoming Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission for discriminating between clouds and aerosols detected in two‐wavelength backscatter lidar profiles. We first analyze single‐test and multiple‐test classification approaches based on one‐dimensional (1‐D) and multidimensional probability distribution functions (PDFs) in the context of a two‐class feature identification scheme. From these studies we derive an operational algorithm. This algorithm is a 3‐D approach utilizing the layer mean attenuated backscatter at 532 nm, the layer‐integrated 1064‐nm to 532‐nm volume color ratio, and the midlayer altitude. A data set acquired by the Cloud Physics Lidar (CPL) is used to test the algorithm. Comparisons are conducted between the 3‐D CALIPSO algorithm results and those derived from an existing 2‐D algorithm. The results obtained show generally good agreement between the two methods. However, of a total of 228,264 layers analyzed, ∼5.7% are classified as different types by the two algorithms. This disparity is shown to be due largely to the misclassification of optically thin clouds as aerosols by the 2‐D algorithm. The use of 3‐D PDFs in the CALIPSO algorithm is found to significantly reduce this type of error because the separation between cloud and aerosol clusters is more complete in this 3‐D space. Dust presents a special case. Because the intrinsic scattering properties of dust layers can be very similar to those of clouds, additional algorithm testing was performed using an optically dense layer of Saharan dust measured during the Lidar In‐space Technology Experiment (LITE). In general, the method is shown to distinguish reliably between dust layers and clouds. The relatively few erroneous classifications that occurred most often in the analysis of the LITE data occurred, in those regions of the Saharan dust layer where the optical thickness was the highest.

Estimate of the global distribution of stratiform supercooled liquid water clouds using the LITE lidar

Supercooled liquid water clouds can occur in the form of thin layers that have a much larger radiative impact than ice clouds of the same water content because of their smaller particle size, yet they are poorly represented in climate models. Such clouds may be easily distinguished from ice by their high lidar backscatter coefficient and sharp backscatter gradient at cloud top. In this paper, data from the Lidar In‐space Technology Experiment (LITE), which flew on the space shuttle in 1994, are used to estimate the fraction of clouds that contain supercooled liquid water over the latitude range ±60°. Around 20% of clouds between −10°C and −15°C were found to contain liquid water, falling with temperature to essentially zero below −35°C. Even from this limited dataset some clear latitudinal clear trends were evident, with a distinctly more frequent occurrence of supercooled water in clouds associated with mid‐latitude weather systems in the southern hemisphere, as well as in tropical clouds warmer than around −15°C. The results between 40 and 60°N agree well with the distribution previously found at Chilbolton in Southern England (51°N), implying that the forthcoming long‐term lidar observations from space will be able to infer the global distribution of mixed‐phase clouds with much greater accuracy and vertical resolution than has been possible until now.

Observations of Typhoon Melissa during the Lidar In-Space Technology Experiment (LITE)

Abstract The Lidar In-Space Technology Experiment (LITE) provided the first high-resolution (15 m) vertical profiling of clouds and aerosols from space. The LITE instrument flew aboard the space shuttle as its prime payload during Space Transportation System (STS)-64 from 9 to 20 September 1994. The lidar obtained vertical profiles of backscatter data at 1.064-, 0.532-, and 0.355-μm wavelengths through a cross section of Typhoon Melissa on 15 and 17 September 1994 during the strengthening and weakening phases of the cyclone. These data provide a unique high-resolution view of aerosols, clouds, and precipitation within the eye, eyewall, and cirrus shield of a tropical cyclone. The data show precipitation cascading from the eyewall into a 27-km-wide eye at the surface, with a clear column of air adjacent to the eyewall and surrounding the boundary layer clouds within the eye. During the weakening phase, the convection is found to be unorganized and weak near the center of circulation. By this time, Typhoon ...

Observations by the Lidar In‐Space Technology Experiment (LITE) of high‐altitude cirrus clouds over the equator in regions exhibiting extremely cold temperatures

Data from the Lidar In‐Space Technology Experiment (LITE) were used to locate clouds near the equatorial tropopause and retrieve temperatures in cloud layers. The experiment was conducted aboard the space shuttle Discovery on September 9–20, 1994. LITE observations over the equator frequently exhibit cloud layers near the tropopause with scattering ratios as high as 2.5 at 532 nm. These clouds have been characterized as cirrus and subvisible cirrus. The clouds were observed near the tropopause with cloud top temperatures ranging from 185 to 200 K. Statistical averages of two optical properties observed by LITE in the 5°N to 15°S latitude band, the wavelength dependence of the extinction due to aerosols (Angstrom coefficient) and scattering ratios, were computed. The Angstrom coefficients show that a significant number (31%) of these high‐altitude cirrus clouds observed by LITE in the 5°N to 15°S latitude band have optical similarities to type 1a polar stratospheric cloud (PSC) particles. Sixty‐six percent of the clouds observed are thin, with scattering ratios ranging from 1.1 to 1.5. Since these clouds are most likely to form at temperatures of 185±2.5 K (a 90% chance), particles of a size and composition similar to type 1a PSCs must be considered a possibility. Since these high‐altitude tropical cirrus clouds may have significant implications for both ozone chemistry and radiative transfer, a closer examination of their composition and phase (using, for example, both in situ methods and depolarization lidar) together with simultaneous meteorological measurements are needed.

Retrieval of stratospheric aerosol size distributions and integral properties from simulated lidar backscatter measurements

A new approach for retrieving aerosol properties from extinction spectra is extended to retrieve aerosol properties from lidar backscatter measurements. In this method it is assumed that aerosol properties are expressed as a linear combination of backscatters at three or fewer wavelengths commonly used in lidar measurements. The coefficients in the weighted linear combination are obtained by minimization of the retrieval error averaged for a set of testing size distributions. The formulas can be used easily by investigators to retrieve aerosol properties from lidar backscatter measurements such as the Lidar In-Space Technology Experiment and Pathfinder Instruments for Clouds and Aerosols Spaceborne Observations.

Fractal properties and denoising of lidar signals from cirrus clouds

Airborne lidar signals of cirrus clouds are analyzed to determine the cloud structure. Climate modeling and numerical weather prediction benefit from accurate modeling of cirrus clouds. Airborne lidar measurements of the European Lidar in Space Technology Experiment (ELITE) campaign were analyzed by combining shots to obtain the backscatter at constant altitude. The signal at high altitude was analyzed for horizontal structure of cirrus clouds. The power spectrum and the structure function show straight lines on a double logarithmic plot. This behavior is characteristic for a Brownian fractal. Wavelet analysis using the Haar wavelet confirms the fractal aspects. It is shown that the horizontal structure of cirrus can be described by a fractal with a dimension of 1.8 over length scales that vary 4 orders of magnitude. We use the fractal properties in a new denoising method. Denoising is required for future lidar measurements from space that have a low signal to noise ratio. Our wavelet denoising is based on the Haar wavelet and uses the statistical fractal properties of cirrus clouds in a method based on the maximum a posteriori (MAP) probability. This denoising based on wavelets is tested on airborne lidar signals from ELITE using added Gaussian noise. Superior results with respect to averaging are obtained.

Retrieval of cloud optical parameters from space-based backscatter lidar data

We present an approach to estimating the multiple-scattering (MS) contribution to lidar return signals from clouds recorded from space that enables us to describe in more detail the return formation at the depth where first orders of scattering dominate. Estimates made have enabled us to propose a method for correcting solutions of single-scattering lidar equations for the MS contribution. We also describe an algorithm for reconstructing the profiles of the cloud scattering coefficient and the optical thickness tau under conditions of a priori uncertainties. The approach proposed is illustrated with results for optical parameters of cirrus and stratiform clouds determined from return signals calculated by the Monte Carlo method as well as from return signals acquired with the American spaceborne lidar during the Lidar In-Space Technology Experiment (LITE).

Multiple scattering effects in the lidar pulse stretching problem

The lidar pulse stretching phenomenon observed during the 1994 Lidar In‐space Technology Experiment (LITE) is investigated in the context of in‐cloud photon multiple scattering processes. The single‐scatter assumption of the standard lidar equation is insufficient for long‐range or wide field‐of‐view applications, where multiple scattering contributions can become significant. These contributions account for the apparent stretching of the lidar return within optically thick media. Using a Monte Carlo approach, the specific roles of cloud optical properties and instrument geometries in determining the magnitude of pulse stretching are examined. Multiple scattering contributions were found to be significant for lidars operating on the space platform, and pulse stretching of the order of that observed in LITE was reproduced over a wide range of cloud optical parameters. This study seeks to both identify and quantify lidar pulse stretching in terms of these driving parameters.

Backscatter-to-Extinction Ratios in the Top Layers of Tropical Mesoscale Convective Systems and in Isolated Cirrus from LITE Observations

Cloud-integrated attenuated backscatter from observations with the Lidar In-Space Technology Experiment (LITE) was studied over a range of cirrus clouds capping some extensive mesoscale convective systems (MCSS) in the Tropical West Pacific. The integrated backscatter when the cloud is completely attenuating, and when corrected for multiple scattering, is a measure of the cloud particle backscatter phase function. Four different cases of MCS were studied. The first was very large, very intense, and fully attenuating, with cloud tops extending to 17 km and a maximum lidar pulse penetration of about 3 km. It also exhibited the highest integrated attenuated isotropic backscatter, with values in the 532-nm channel of up to 2.5 near the center of the system, falling to 0.6 near the edges. The second MCS had cloud tops that extended to 14.8 km. Although MCS2 was almost fully attenuating, the pulse penetration into the cloud was up to 7 km and the MCS2 had a more diffuse appearance than MCS1. The integrated backscatter values were much lower in this system but with some systematic variations between 0.44 and 0.75. The third MCS was Typhoon Melissa. Values of integrated backscatter in tt-ds case varied from 1.64 near the eye of the typhoon to between 0.44 and 1.0 in the areas of typhoon outflow and in the 532-nm channel. Mean pulse penetration through the cloud top was 2-3 km, the lowest penetration of any of the systems. The fourth MCS consisted of a region of outflow from Typhoon Melissa. The cloud was semitransparent for more than half of the image time. During that time, maximum cloud depth was about 7 km. The integrated backscatter varied from about 0.38 to 0.63 in the 532-nm channel when the cloud was fully attenuating. In some isolated cirrus between the main systems, a plot of integrated backscatter against one minus the two-way transmittance gave a linear dependence with a maximum value of 0.35 when the clouds were fully attenuating. The effective backscatter-to-extinction ratios, when allowing for different multiple-scattering factors from space, were often within the range of those observed with ground-based lidar. Exceptions occurred near the centers of the most intense convection, where values were measured that were considerably higher than those in cirrus observed from the surface. In this case, the values were more compatible with theoretical values for perfectly formed hexagonal columns or plates. The large range in theoretically calculated back- scatter-to-extinction ratio and integrated multiple-scattering factor precluded a closer interpretation in terms of cloud microphysics.

Impact of cirrus cloud ice crystal shape and size on multiple scattering effects: Application to spaceborne and airborne backscatter lidar measurements during LITE Mission and E LITE Campaign

Forward scattering in cirrus clouds can significantly affect backscatter lidar signal. Its contribution can be estimated numerically knowing the size and shape of the crystals. Contemporary airborne and space‐borne lidar measurements collected during the European Lidar In‐space Technology Experiment (E‐LITE) field campaign (in the framework of the NASA/LITE mission) are used to show that forward scattering reduces the optical depth derived from space‐borne measurements by at least a factor of 2 with respect to the true value. This reduction factor is discussed in terms of crystal size and shape (i.e. forward scattering, and measurement configuration). It is shown that cirrus backscatter‐to‐extinction ratios derived from airborne and space‐borne lidar measurements can be used to illustrate the sensitivity of multiple scattering effects the ice crystal size and shape.

Validation of the Saharan Dust Plume Conceptual Model Using Lidar, Meteosat, and ECMWF Data

Lidar observations collected during the Lidar In-space Technology Experiment experiment in conjunction with the Meteosat and European Centre for Medium-Range Weather Forecasts data have been used not only to validate the Saharan dust plume conceptual model constructed from the GARP (Global Atmospheric Research Programme) Atlantic Tropical Experiment data, but also to examine the vicissitudes of the Saharan aerosol including their optical depths across the west Africa and east Atlantic regions. Optical depths were evaluated from both the Meteosat and lidar data. Back trajectory calculations were also made along selected lidar orbits to verify the characteristic anticyclonic rotation of the dust plume over the eastern Atlantic as well as to trace the origin of a dust outbreak over West Africa. A detailed synoptic analysis including the satellite-derived optical depths, vertical lidar backscattering cross section profiles, and back trajectories of the 16–19 September 1994 Saharan dust outbreak over the easte...