RESUMEN
We report the first (to our knowledge) field demonstration of simultaneous wind and temperature measurements with a Na double-edge magneto-optic filter implemented in the receiver of a three-frequency Na Doppler lidar. Reliable winds and temperatures were obtained in the altitude range of 10-45 km with 1 km resolution and 60 min integration under the conditions of 0.4 W lidar power and 75 cm telescope aperture. This edge filter with a multi-frequency lidar concept can be applied to other direct-detection Doppler lidars for profiling both wind and temperature simultaneously from the lower to the upper atmosphere.
RESUMEN
A coherent Doppler lidar system was frequency stabilized in a master-slave configuration by a phase-modulation technique. The short-term frequency stability, ~0.2 MHz rms, was maintained in a vibrational environment on a ship during a field campaign in the tropical Pacific Ocean. The long-term frequency stability was <2.6 kHz/h. Thus, in many applications, shot-to-shot frequency correction can be disregarded, which will result in increased speed and simplicity of the data-acquisition system. A frequency chirp could not be detected. These properties permit Doppler wind measurements with high efficiency and duty cycles to be made, even on airborne and spaceborne platforms.
RESUMEN
An optical technique is described that determines the path-averaged value of a refractive-index structure parameter at 10.6 microm by use of a pulsed coherent CO(2) lidar in direct detection and hard-target returns. The lidar measurements are compared with measurements taken by a 0.9-microm scintillometer and temperature probe (with humidity corrections). The experimental results show good agreement for C(n)(2) >or= (-14) m(-2/3). With respect to practical applications the new technique permits C(n)(2) lidar measurements in a neutral meteorological situation to an unstably stratified convective boundary layer over long ranges (1 km or more).
RESUMEN
The atmospheric lidar remote sensing groups of NOAA Environmental Technology Laboratory, NASA Marshall Space Flight Center, and Jet Propulsion Laboratory have developed and flown a scanning, 1 Joule per pulse, CO2 coherent Doppler lidar capable of mapping a three-dimensional volume of atmospheric winds and aerosol backscatter in the planetary boundary layer, free troposphere, and lower stratosphere. Applications include the study of severe and non-severe atmospheric flows, intercomparisons with other sensors, and the simulation of prospective satellite Doppler lidar wind profilers. Examples of wind measurements are given for the marine boundary layer and near the coastline of the western United States.
RESUMEN
We investigate the ability of detection techniques based on the likelihood ratio to discriminate between heterodyne lidar Doppler estimates at low signal levels using examples generated by simulation. The distinction between estimates that are regarded as acceptable and as spurious is based on the Cramer-Rao lower bound. The conditional false alarm probability, which ordinarily describes recording detection of a signal when none is present, is then found to be an approximate upper bound on the probability of selection of a spurious estimate. The method is superior theoretically to similar techniques based on detection functions other than the likelihood ratio. The likelihood ratio also provides a basis for reprocessing rejected data in the light of contextual information provided by those estimates that are accepted.
RESUMEN
Heterodyne lidar estimates are a function of a number of experimental parameters, some of which can be adjusted or tuned to optimize statistical precision. Here we refer the precision to the theoretical limit for optical measurements of return power and Doppler shift and investigate the conditions for optimization using established theoretical expressions for the standard deviation of various estimates. Tuning is characterized by a degeneracy parameter (the photocount per fade). For estimators that filter or resolve the return, it is shown that optimal tuning is achieved at wideband signal-to-noise ratios less than 0 dB and detected signal levels corresponding to more than a single effective photocount. Estimators that do not filter are predictably at a disadvantage when the signal bandwidth range gate product is low. The minimum standard deviation available from an optimally tuned heterodyne system is found to be greater than twice the limit.
RESUMEN
A multibeam transmitter provides the flexibility to change the overlap function and range response function of monostatic incoherent lidar systems. A nearly flat range response and a close near-range coverage can be achieved simultaneously, even under different atmospheric conditions. Such a significant improvement in range response will solve the problem of detector overexposure by near-range atmosphere-backscattered radiation (which leads to nonlinear response, saturation, or even damage of the detector), and will significantly reduce the dynamic range of the detector output signal, thus reducing quantization error of the digitizer. Consequently, the accuracy of lidar measurements, especially that of differential absorption lidar measurements, will be improved.
RESUMEN
The receiving efficiency eta as a function of range z is investigated for pulsed coherent lidars using a theory that relates eta(z) to the transmitted laser intensity and the point-source receiving efficiency eta(s)(r,z). The latter can be calculated either by a forward method, or by a backward method that employs the back-propagated local oscillator (BPLO) approach. The BPLO method is efficient and accurate provided that cascaded diffraction effects inside the lidar system are properly taken into account. The theory is applied to the ideal case to examine the optimization of the system when both transmitted and BPLO fields at the antenna are Gaussian, including optimum telescope aperture.
RESUMEN
Using the theory developed in Part 1, the receiving efficiency as a function of range, eta(z), is calculated under different conditions for the NOAA/ERL/Wave Propagation Laboratory CO(2) Doppler lidar. Theoretical analyses, numerical calculations, and experimental measurements are carried out to quantify the sensitivity of eta(z) to transmitted laser beam quality, telescope focal setting, telescope power, scanner astigmatism, LO beam divergence, and system misalignment. These results bring insight to the design of practical coherent lidar systems.
RESUMEN
The use of recursive techniques based on Kalman filter algorithms for identification of time series system models for Doppler lidar returns and the subsequent filtering and smoothing of measured data is explored. The form of possible stochastic system models is reviewed, and reiterative maximum likelihood and innovation spectral tests are used for identification. It is found that a random walk model is adequate for the returns here, and possible explanations for this are considered. Examples are given to illustrate the extension of our method to real-time applications and on-line outlier rejection.
RESUMEN
Recursive estimation of nonlinear functions of the return power in a lidar system entails use of a nonlinear filter. This also permits processing of returns in the presence of multiplicative noise (speckle). The use of the extended Kalman filter is assessed here for estimation of return power, log power, and speckle noise (which is regarded as a system rather than a measurement component), using coherent lidar returns and tested with simulated data. Reiterative processing of data samples using system models comprising a random walk signal together with an uncorrelated speckle term leads to self-consistent estimation of the parameters.
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The convolution effect in aerosol backscattered CO(2) coherent lidar returns caused by the long tail of the laser pulse is analyzed by modifying the original lidar equation and introducing a correction function C(r)(R). The characteristics of the correction function and its effect on differential absorption lidar water vapor measurements are investigated for coherent lidars. A deconvolution technique is developed consisting of a leastsquares fitting and iteration procedure for retrieval of the mean value of the atmospheric backscattering coefficient beta and a reverse filtering procedure for estimating the fluctuation components of the beta profile. Data obtained with the WPL coherent CO(2) lidar are reanalyzed using the above method, giving improved estimates of the structures and the mean water vapor content.
RESUMEN
A CO(2) heterodyne lidar system and high speed digitizer were used to examine properties of returns from disk and belt-type calibration targets and atmospheric aerosols. Amplitude statistics of the returns from the targets examined corresponded to those of the Rayleigh phasor predicted by theory. Returns from a belt sander fluctuated at a much slower rate than those from the disks or aerosols, requiring longer averaging times for accurate power measurement. At very close focal lengths returns from single large particles often domier nated the backscattered aerosol signal.
RESUMEN
We determine the backscatter reflectance (more properly the bidirectional reflectance distribution function at a 45 degrees angle of incidence and observation) for circularly polarized radiation of lambda = 10.6 microm for 120-grit aluminum oxide sandcloth (1.5 x 10(-2) sr(-1)) and 400-grit silicon carbide sandpaper (1.1 x 10(-2) sr(-1)) with respect to sublimed flowers of sulfur (1.8 x 10(-1) sr(-1)). The effect of range and the atmospheric effect of turbulence-induced beam wander are discussed for both rotating disks and linearly translated belts. The advantages of large slowly rotating disks for field calibrations are presented.