Time-dependent attenuator for dynamic range reduction of lidar signals

Expanding the dynamic range of a lidar receiver by the method of dynode-signal collection

A method of lidar data collection by simultaneous registration of signals from the anode and several dynodes of the photomultiplier is suggested. The dynamic range of the receiver has been extended as many as 5 orders of magnitude in the case of cloud sensing. The stable operation under strong background illumination is possible without losses in fine signal structure.

Future performance of ground-based and airborne water-vapor differential absorption lidar. I. Overview and theory

The performance of a future advanced water-vapor differential absorption lidar (DIAL) system is discussed. It is shown that the system has to be a direct-detection system operating in the rhovarsigmatau band of water vapor in the 940-nm wavelength region. The most important features of the DIAL technique are introduced: its clear-air measurement capability, its flexibility, and its simultaneous high resolution and accuracy. It is demonstrated that such a DIAL system can contribute to atmospheric sciences over a large range of scales and over a large variety of humidity conditions. An extended error analysis is performed, and errors (e.g., speckle noise) are included that previously were not been discussed in detail and that become important for certain system designs and measurement conditions. The applicability of the derived equation is investigated by comparisons with real data. Excellent agreement is found.

Lidar-signal compression by photomultiplier gain modulation: influence of detector nonlinearity

The application of photomultiplier gain modulation to the compression of wide-dynamic-range lidar signals is investigated in relation to the effect of the gain level on anode-signal linearity. Gain reduction is achieved by the coupling of modulation signals through either multidynode or focus-grid gating networks. This technique facilitates signal recovery and prevents detector nonlinearity and dynode damage caused by high near-field lidar signals. The measurements were performed in the current mode primarily on a 50-mm-diameter, 12-stage photomultiplier (EMI 9214) with a bialkali photocathode. With 3- or 4-dynode-based modulation made at a photomultiplier voltage of 1300 V and a gain of 1 x 10(7), signals of ~6 mA can be maintained at the 1% linearity limit from 100% to 0.2% modulation, corresponding to a 500-fold reduction in the lidar-signal dynamic range. A significant advantage to dynode modulation is that it preserves the shot-signal-to-noise ratio of the incoming signal, which is not true for focus-grid modulation or external predetection schemes such as controlled obscuration or Pockels-cell modulation that attenuate the as-yet unamplified signal.

Ground-based differential absorption lidar for water-vapor profiling: assessment of accuracy, resolution, and meteorological applications

The accuracy and the resolution of water-vapor measurements by use of the ground-based differential absorption lidar (DIAL) system of the Max-Planck-Institute (MPI) are determined. A theoretical analysis, intercomparisons with radiosondes, and measurements in high-altitude clouds allow the conclusion that, with the MPI DIAL system, water-vapor measurements with a systematic error of <5% in the whole troposphere can be performed. Special emphasis is laid on the outstanding daytime and nighttime performance of the DIAL system in the lower troposphere. With a time resolution of 1 min the statistical error varies between 0.05 g/m(3) in the near range using 75 m and-depending on the meteorological conditions-approximately 0.25 g/m(3) at 2 km using 150-m vertical resolution. When the eddy correlation method is applied, this accuracy and resolution are sufficient to determine water-vapor flux profiles in the convective boundary layer with a statistical error of <10% in each data point to approximately 1700 m. The results have contributed to the fact that the DIAL method has finally won recognition as an excellent tool for tropospheric research, in particular for boundary layer research and as a calibration standard for radiosondes and satellites.