GB1529624A - Detection of atmospheric activity - Google Patents

Abstract

1529624 Detecting atmospheric electrical activity DYTRONICS CO Inc 9 Jan 1976 [10 Jan 1975] 00864/76 Heading H4D A system for mapping electrical storms receives electromagnetic signals in a predetermined frequency band from electrical activity in a storm, processes the received signals to give further signals of amplitude inversely related to that of the received signals, and uses the processed signals to drive a display. Thus received signals of high amplitude are represented in the display further from the display origin than are received signals of low amplitude. Assuming that the electromagnetic signals are of uniform strength at their source, the processing accounts for their attenuation with range from the receiver and the display will represent such range. In the Fig. 4A embodiment, electric and magnetic components of the e-m signals from lightning are detected by antenna 10 and crossed loop antennae 11, 12 respectively. Signals from the loop antennae are "correlated" at 16, 17 with the antenna 10 signal to discriminate against noise. Signals Ex, Ey, representing the magnetic field strength components in orthogonal directions, are obtained by integration at 18,19 over periods set by timers 20 in response to the sum of the signals from 11, 12 exceeding a threshold value set at 22. The thresholding serves to distinguish signals due to main lightning strokes from unwanted signals due to preceding leader strokes. In "foldback" unit 24 the signals Ex, Ey are effectively divided by E R <SP>2</SP>, the square of the sum of the signals from 11,12, to give the processed signals which, after storage in recirculating shift register memories 26, control the deflections of a CRT display 28 to produce a display spot at a position corresponding to the azimuth and approximate range of the the lightning discharge. If the system is to be used on an aircraft, motion of the aircraft will make the display inaccurate due to the changing range. To overcome this, old data are erased from memories 26 if they are not being up-dated fast enough by successive lightning discharges; alternatively the memory contents may be decremented, at a rate chosen with regard to the speed of the aircraft, so that the display "creeps" in one dimension to compensate for the motion. The foldback processing may be analogue (e.g. optical) or digital. Details are given of digital foldback processing (Figs. 8A and 8B, not shown) and of circuits for the motion compensation (Figs. 10A-10F, not shown). The memory and display functions may be combined, e.g. by using a storage tube, LED or liquid crystal display.