Jean-Yves Delahaye

A New Shipborne Microwave Refractometer for Estimating the Evaporation Flux at the Sea Surface

Abstract After a brief description of humidity measurement and a short presentation of methods of microwave refractometry for evaporation flux, a new X-band refractometer system is presented. Based on a new design and a new material for the microwave cavity, it does not need calibration for refractive index variations because of its reduced thermal time constant. The new device has been combined with a sonic anemometer and traditional mean meteorological measurements on a 12-m shipborne mast. It has been found to be very efficient for obtaining humidity fluctuations and fluxes in the CATCH 97 (Couplage avec l’ATmosphere en Conditions Hivernales) and FETCH 98 (Flux, Etat de la mer et Teledetection en condition de fetCH variable) experiments under various wind and stability conditions. The inertial subrange is of very high quality. To first order, the evaporation flux and refractive index flux are very similar. In extreme meteorological conditions, such as those encountered during CATCH, the sensible heat f...

Combining signal processing and machine learning techniques for real time measurement of raindrops

The data acquisition system for a new type of optical disdrometer is presented. As the device must measure sizes and velocities of raindrops as small as 0.1 mm diameter in real time in the presence of high noise and a variable baseline, algorithm design has been a challenge. The combining of standard signal processing techniques and machine learning methods (in this case, a neural network) has been essential to obtaining good performance.

Design of a High-Velocity Extremum Controller

A new kind of extremum control system is described. The system has a single-input controlled process with input and output disturbances and an output lag. The equations of the system are designed in order to follow with a great efficiency the variations of the extremum. The control signal is mainly generated by multiplying the derivatives of the controlled process input and output. In order to eliminate the solution of the equations which corresponds to the system drift, two particular circuits were added. Computed and experimental results demonstrate that the theoretical model is realistic enough to be used as a design tool. For an output lag of 1 ms and a disturbance velocity of 1 percent per ms, the extremum controller measures the maximum with a time resolution of 0.5 ms and an error of 0.3 percent.