Heterodyne Laser Radar Research Articles

Squeezing the local oscillator does not improve signal-to-noise ratio in heterodyne laser radar

The signal-to-noise ratio for heterodyne laser radar with a coherent target-return beam and a squeezed local-oscillator beam is lower than that obtained using a coherent local oscillator, regardless of the method employed to combine the beams at the detector.

Laboratory validation of range-resolved reflective tomography signal-to-noise expressions

The Air Force Phillips Laboratory is in the process of demonstrating an advanced space surveillance capability with a heterodyne laser radar (ladar) system. Notable features of this ladar system include its narrow micropulses (<1.5 ns) contained in a pulse-burst wave form that allows high-resolution range data to be obtained and its high power (30 J/pulse burst) that permits reasonable signal returns from satellites. Recently, time-resolved image-domain signal-to-noise ratios have been derived for both the intensity projections calculated from the range-resolved reflective data and image information obtained with linear combinations of the projections. In this paper the signal-to-noise expression for intensity projections is validated by laboratory data.

Reflective tomography using a short-pulselength laser: system analysis for artificial satellite imaging

The Air Force Phillips Laboratory is in the process of demonstrating an advanced space surveillance capability with a heterodyne laser radar (ladar) system. Notable features of this ladar system include its narrow (< 1.5 ns) micropulses, contained in a pulse-burst waveform that allows high-resolution range data to be obtained, and its high power (30 J in a pulse burst), which permits reasonable signal returns from satellites. The usefulness of these range data for use in reflective tomographic reconstructions of satellite images is discussed. A brief review of tomography is given. Then it is shown that the ladar system is capable of providing adequate range-resolved data for reflective tomographic reconstructions in terms of range resolution and sampling constraints. Mathematical expressions are derived which can be used to convert the ladar returns into reflective projections. Image reconstructions from computer-simulated data which include the effects of laser speckle and photon noise are presented and discussed. These reconstructions contain artifacts even in the absence of noise, due to the inadequacies of the standard tomographic problem formulation to accurately model the reflective projections obtained from the ladar system. However, object features can still be determined from the reconstructions when typical noise levels are included in the simulation.

Signal-to-noise-ratio equations for a heterodyne laser radar

We analyze the signal-to-noise-ratio equations for a heterodyne laser radar with identical transmit and receive optics. We defines the beam-profile efficiency, a quantity that must be maximized to optimize a system design. This calculation can be used to evaluate a system in both near and far fields for focused and nonfocused systems. The beam-profile efficiency can be evaluated in many ways, and we describe one possible solution. Using this solution, we present the results of an actual system evaluation.

Method for calibrating heterodyne receiver arrays

Modification of the transmitter section of a heterodyne laser radar to include two additional output beams at appropriate offset frequencies makes calibration of the local oscillator phases of a multichannel receiver possible.

Infra-red heterodyne laser radar for remote sensing of air pollutants by range-resolved differential absorption

An infra-red heterodyne laser radar scheme incorporating range-resolved differential absorption using elastically backscattered, pulsed signal from distributed particles in the atmosphere is proposed and analysed. The basic requirements of the system arrangement and operating parameters involved in this scheme are discussed in detail. This method is shown to offer a remote and spatially-resolved measurement of various molecuar pollutants dispersed in the air for ranges up to several km and detection sensitivities to less than 0.1 ppm with laser pulses of 100 W average power. This power is 103 to 106 times smaller than that required with the conventional direct detection technique in the infra-red. The measuring accuracy and its limiting processes inherent to the infra-red range-resolved differential absorption method are also analysed.

Infrared laser radar technique using heterodyne detection for range-resolved sensing of air pollutants

An infrared, pulsed heterodyne laser radar using differential absorption technique with tunable lasers is proposed as a practical means of measuring dispersed air pollutants with range resolution. A system analysis shows that this scheme offers an adequate sensitivity for ranges up to several km.