Although laser remote sensing techniques have been applied to a variety of environmental measurement tasks for several decades, it has not been until relatively recently that the promise held by lidar and laser radar has begun to be exploited for global measurements from an Earth-orbiting vantage point. Notwithstanding the successful demonstration of highresolution laser altimetry and cloud/aerosol profiling from orbital platforms in the last decade, full realization of the potential for these techniques to address important Earth science questions awaits the availability of next generation instruments incorporating durable, high-performance laser transmitters and advanced receiver technologies. Some of the most critical, high-impact Earth science measurement applications are enabled by lidar techniques - in some cases uniquely so. This paper describes some of these scenarios and also the philosophy underlying the investment that the US National Aeronautics and Space Administration (NASA) is making in order to pro-actively accelerate technology development in certain key areas that will contribute to our future ability to field advanced laser remote sensing instrumentation in space.

The Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) is the primary instrument on the CALIPSO satellite, which is scheduled to launch in 2005. CALIOP will provide profiles of total backscatter at two wavelengths, from which aerosol and cloud profiles will be derived. The instrument also measures the linear depolarization of the backscattered return, allowing discrimination of cloud phase and the identification of the presence of non-spherical aerosols. CALIOP is complete and has been tested in a ground-based configuration. This paper provides information on basic characteristics and performance of CALIOP.

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite will be launched in April of 2005, and will make continuous measurements of the Earth's atmosphere for the following three years. Retrieving the spatial and optical properties of clouds and aerosols from the CALIPSO lidar backscatter data will be confronted by a number of difficulties that are not faced in the analysis of ground-based data. Among these are the very large distance from the target, the high speed at which the satellite traverses the ground track, and the ensuing low signal-to-noise ratios that result from the mass and power restrictions imposed on space-based platforms. In this work we describe an integrated analysis scheme that employs a nested, multi-grid averaging technique designed to optimize tradeoffs between spatial resolution and signal-to-noise ratio. We present an overview of the three fundamental retrieval algorithms (boundary location, feature classification, and optical properties analysis), and illustrate their interconnections using data product examples that include feature top and base altitudes, feature type (i.e., cloud or aerosol), and layer optical depths.

Using a combination of two modest sized coherent and direct detection Doppler lidars may offer significant advantages over the single detection method approaches. All space-based Doppler wind lidar proposed missions to date have been based upon a single detection scheme, either coherent (WINDSAT, LAWS, SPARCLE, JEM/CDL) or direct (Zephyr, ALADIN, ADM) detection. A hybrid detection wind lidar has been proposed and is undergoing a feasibility study. The hybrid wind lidar is currently being baselined for an airborne test bed and is funded for a weather forecasting impact evaluations at NOAA and NASA.

It has been realized that eye-safe 2-mm all-solid-state lasers are important laser sources for an accurate measurement of the CO2 concentration in the atmosphere. Served as laser transmitters, they can be integrated into ground-based, airborne-base, and spaceborne-based CO2 Differential Absorption Lidars (DIALs) to accomplish the measurement. In addition, the lasers are also ideal laser pumping sources for a ZnGeP₂ (ZGP) Optical Parametric Oscillator (OPO) or an Optical Parametric Amplifier (OPA) to achieve tunable laser output in 3~5 mm. In this spectrum region, the other important greenhouse gases, water vapor (H₂O), carbon monoxide (CO), and methane (CH₄) in the atmosphere can be measured. In this paper, we report a diode-pumped, double-pulsed, Q-switched, eye-safe Ho:Tm:LuLF laser at 2.05 mm developed for ground-based and airborne-based CO₂ Differential Absorption Lidars (DIALs). The technology can be easily transferred to a space-borne CO₂ DIAL in the future. The total output pulse energy of the laser is 220 mJ and 204 mJ per pair of pulses at 2 Hz and at 10 Hz respectively. The related optical energy conversion efficiency is 6.7% and 5.9% respectively.

Obtaining accurate wind observations from an airborne Doppler lidar requires very precise pointing knowledge of the laser beam. A .1 degree pointing knowledge error can result in a .2 m/s velocity error along the line-of-sight. One option is to exercise great care in aligning the laser beam with the aircraft axes and then acquiring precise information from an onboard navigation system for aircraft attitude. A pointing knowledge approach using surface returns developed for a space mission has been adapted to the CIRPAS Twin Otter's Doppler wind lidar and has been demonstrated during a series of field experiments. RMSEs less than .05 m/s have been achieved for the three components of the wind in vertical profiles (50 m resolution) representing a few 100 meters of flight path. This approach negates the need for precise physical alignment and allows for continuous up dating of attitude corrections due to aircraft flexure, air stream loading of the scanner or any drift in the Inertial Navigation System. Examples of soundings and algorithm validation are presented along with applications where the vertical velocity data are evaluated for their realism.

We describe a technique for estimating the parameters of small-scale wind turbulence from the wind velocity measured with a pulsed solid -state- and CO₂-laser-based coherent Doppler lidar. We present the algorithm for simulation of return signals of pulsed 2mkm and 10.6 mkm CDLs along with the methods for estimation of the wind turbulence parameters from the spatial structure function of wind velocity measured by CDL in the cases of both short separations between measurement points (2mkm CDL) and long ones (10.6 mkm CDL). The errors in estimation of the turbulent parameters from the lidar data are determined as functions on the signal storage time.

In studies of the internal boundary layer, it is important to make the lidar both eye-safe and capable of measuring near range extinction to high accuracy. The inversion of data is much more challenging due to the weaker signal from an eye-safe lidar. The method of inversion employed in this paper is the Fernald's method. Because the digitization system is capable of obtaining returns in the time interval of a few seconds, formal statistical analysis and error propagation are introduced in the inversion. Different weighting schemes are used during the averaging of the inversion and the results from scattered cloud data as well as pure aerosol profiles will be discussed. Results from several sites and under different meteorological conditions will be reported.

The main objective of the paper is to demonstrate rare-earth (Tm³⁺, Er³⁺, Ho³⁺) and transition-metal ion (Cr-ion) doped glass fibres as potential broadly tunable laser devices. The paper will discuss the spectroscopy of metal ions and suitability of glass hosts for designing efficient devices, which can be pumped using commercially available semiconductor or fibre-based IR laser sources, e.g. at 800, 980, 1020, 1040, and 1480 nm wavelengths. The spectroscopic properties of transition metal ion-host systems are compared briefly with those of crystal based devices. Results of the measured spectroscopic properties for Cr-ion and rare-earth ion doped fibre systems particularly pumped using NIR wavelength from Ti-sapphire sources are also reported.

BAE SYSTEMS reports on a program to develop a high-fidelity model and simulation to predict the performance of angle-angle-range 3D flash LADAR Imaging Sensor systems. 3D Flash LADAR is the latest evolution of laser radar systems and provides unique capability in its ability to provide high-resolution LADAR imagery upon a single laser pulse; rather than constructing an image from multiple pulses as with conventional scanning LADAR systems. However, accurate methods to model and simulate performance from these 3D LADAR systems have been lacking, relying upon either single pixel LADAR performance or extrapolating from passive detection FPA performance. The model and simulation developed and reported here is expressly for 3D angle-angle-range imaging LADAR systems. To represent an accurate "real world" type environment, this model and simulation accounts for: 1) laser pulse shape; 2) detector array size; 3) atmospheric transmission; 4) atmospheric backscatter; 5) atmospheric turbulence; 6) obscurants, and; 7) obscurant path length. The angle-angle-range 3D flash LADAR model and simulation accounts for all pixels in the detector array by modeling and accounting for the non-uniformity of each individual pixel in the array. Here, noise sources are modeled based upon their pixel-to-pixel statistical variation. A cumulative probability function is determined by integrating the normal distribution with respect to detector gain, and, for each pixel, a random number is compared with the cumulative probability function resulting in a different gain for each pixel within the array. In this manner very accurate performance is determined pixel-by-pixel. Model outputs are in the form of 3D images of the far-field distribution across the array as intercepted by the target, gain distribution, power distribution, average signal-to-noise, and probability of detection across the array. Other outputs include power distribution from a target, signal-to-noise vs. range, probability of target detection and identification, and NEP vs. gain.

It has recently been shown that lidar (LIght Detection And Ranging) can effectively detect smoke plumes from small bonfires up to distances of 6.5 km, so that the technique can be used for wildfire surveillance. The aim of the present work is to describe a method for calculating the optimal location and minimum number of lidar stations required for the surveillance of a given forest area, taking the hilly terrain of Sintra-Cascais Nature Park (Portugal) as an example. The placement and horizontal scanning of the lidar sensors must be such that the laser beam passes over the ground, while keeping sufficiently low to enable early smoke plume detection, before the smoke is dispersed by the wind. Simultaneously, the laser beam should not hit the ground at distances shorter than the instrument range. To solve the problem, a terrain rendering was created and the best laser-beam zenith angle for each azimuth and the effective range covered by each lidar were calculated. The computations showed that 95.2% of the 146 km² of the Nature Park area can be covered by seven detectors with the laser beams scanning at a height of 50 m or less above ground.

Characteristics of object images observed through scattering media with an active vision system with wide receiving angle operating in the mode of spatial selection are estimated using the Monte Carlo method. The effect of optical and geometrical conditions of observation on the contrast in images of reflecting objects is considered. Interpretation is given to the obtained dependences. The main results obtained in this work are the following. A suit of programs of the Monte Carlo method has been developed for statistical simulation of the imaging process in pulsed active vision systems with spatial selection. In the framework of the considered formulation of the problem, the contrast of the object image against the scattered background and the surface lying under the observation path exceeds the level of 0.8 up to the optical depth of the medium τ ≈ 4 and exceeds 0.4 up to τ ≈ 5. The process of multiple scattering determines, to the significant degree, not only the backscattering, but also the useful signal and, in particular, the intensity of the non-scattered radiation reflected by the object and recorded by the receiver. The sample of the ladar for car application was created and got testing.

The purpose of this paper is to describe a new proved multi-channel laser-radar technology which enables several thousands of high-sensitive laser-radar or lidar receivers to be integrated on a fingernail-sized CMOS-chip for fast 3D-perception and, furthermore, to explain the huge number of resulting applications and to estimate the desirable scientific, economic and society impacts. These extraordinary capabilities rely on the revolutionary improvements introduced by a smart inherently-mixing photodiode with two controllable photo-current outputs [1]. We call it PMD (Photonic Mixer Device) because the opto-electronic mixing process is accomplished directly in the photonic state, followed by an integration process to get OE-correlation and the delay of the optical echo and the modulation signal. The PMD-principle provides an unbelievable simplification, size-reduction and improvement in Multi-Channel Light Detecting and Ranging as a MC-PMD-Lidar or 3D-PMD-camera without scanner. Thanks to the competence and merit of the PMDTechnologies GmbH in cooperation with the INV of the University of Siegen finally brought the PMD in big steps to reliability and to large pixel numbers and to products with today about 20.000 lidar receivers in a 120x160 PMD-matrix, which exhibits homogenous and exquisite specifications like very constant mean value and low standard deviation compared with conventional radar receivers. This innovation may be seen as a breakthrough in the history of camera development. The "3D-camera" of today comprises more 3D-pixels in a PMD-array than, about 1970, the first CCD-cameras contained 2D-pixel in a CCD-array. Both are of similar size aside from the modulated sender with integrated LED's or laser diodes required for a homogenous illumination of the field-of-view.

The diffractive bidirectional reflectance distribution function (BRDF) of a surface with one-dimensional roughness is derived from coherence theory using an expansion valid for large effective roughness. Expansion of the surface autocorrelation function in the limit leads to representative Cauchy and Gaussian BRDFs and an intermediate closed-form general solution, which is fit to specular-plane BRDF data from an aluminum satellite sample at the wavelengths 1.06 microns and 10.6 microns.

We are presenting of a photon counting laser altimeter simulator. The simulator is designed to be a theoretical and numerical complement for a Technology Demonstrator of the space born laser altimeter for planetary studies built on our university. The European Space Agency has nominated the photon counting altimeter as one of the attractive devices for planetary research. The device should provide altimetry in the range 400 to 1400 km with one meter range resolution under rough conditions - Sun illumination, radiation, etc. The general altimeter concept expects the photon counting principle laser radar. According to this concept, the simulator is based on photon counting radar simulation, which has been enhanced to handle planetary surface roughness, vertical terrain profile and its reflectivity. The simulator is useful complement for any photon counting altimeter both for altimeter design and for measured data analysis. Our simulator enables to model the orbital motion, range, terrain profile, reflectivity, and their influence on the over all energy budget and the ultimate signal to noise ratio acceptable for the altimetry. The simulator can be adopted for various air or space born application.

Aerosols are among the most spatially variable components of the atmosphere, and thus their study requires their monitoring over a broad geographic range. The backscattering of light from suspended solid and liquid particles in the atmosphere obeys Mie scattering theory. Light attenuation in the spectral region from 300 to 4000 nm due to Mie scattering exceeds that due to molecular (Rayleigh) scattering and ozone absorption combined. This occurs despite the fact that aerosol particle concentrations in the atmosphere are many orders of magnitude smaller than molecular concentrations. Starting from the characteristics of urban aerosols measured over the city of Popayan (Colombia), 2° 27’ N; 76° 37' W, with a PM10 particle selector, we present the results of a study of light attenuation properties generated using Matlab computer code, to simulate and predict measurements with a Lidar system operating at 514.5 nm.

We are presenting experimental data on atmospheric fluctuations measurements and their influence on laser ranging precision. Three independent path configurations have been studied: 4.3-kilometer horizontal path, slant path at elevation 10-80 degrees and slant path from ground to space. The laser ranging has been performed using the satellite laser ranging system in Graz, Austria. The system precision is 6 picoseconds (single shot RMS) and the measurement repetition rate is 2 kHz. That enables us to monitor fast fluctuations with period of the order of milliseconds. The atmospheric seeing conditions have been measured simultaneously. We have identified and measured contribution of the atmospheric fluctuations to the ranging precision and time spectrum of these fluctuations for the first time.

We are presenting preliminary results of the development of the Technology Demonstrator of the photon counting laser altimeter for planetary studies. This device is expected to be a universal instrument applicable in various space missions. The device should provide altimetry and surface radiometry in the range of 400 to 1400 km with one meter range resolution under rough conditions - Sun illumination, space radiation, etc. The Technology Demonstrator is the modular test equipment dedicated to test individual critical components, concepts and technologies: the laser source, the photon counting detector and its electronics. The concept and techniques to be investigated are: the energy budget of the altimeter, range resolution, the signal to noise ratio under various background light conditions, photon counting data acquisition, signal mining and processing techniques.

Remote-sensing technology for weathering assessment should be sensitive to both textural and compositional changes in a surface. The capabilities of active polarimetry in weathering assessment are investigated through measurements of the Mueller matrices of bare and painted metal and dielectric surfaces at visible laser wavelengths in the quasi-monostatic geometry. Weathering mechanisms investigated include particulate erosion and solar irradiation, which are found to alter certain off-diagonal Mueller elements by around 5% in measurements over illumination angle.

The lidar equation uncertainty, caused by the presence of two unknown functions (extinction and backscatter coefficients), is the main source of measurement errors in the elastic lidar searching of the atmosphere. The multiangle data-processing technique that applies the layer-integrated form of the angle-dependent lidar equation, allows one to avoid the a priori selection of the extinction-to-backscatter ratio. However, the practical use of the technique is impeded by atmospheric horizontal heterogeneity and distortions in real lidar data, which worsen the inversion accuracy of the retrieved extinction-coefficient profiles; in addition, the multiangle solution is extremely sensitive even to minor systematic distortions in the inverted data. A combination of the one-directional and multiangle data-processing technique improves the measurement accuracy of the retrieved data. Here no guesses are required about the vertical profile of the extinction-to-backscatter ratio. The technique was developed and tested with experimental data using a two-wavelength scanning lidar at the Fire Sciences Laboratory in Missoula, MT, USA. The specifics, advantages, and restrictions of this combined technique are discussed and illustrated by both synthetic and experimental data.