| 摘要 |
<p>The total range to be explored consists of a succession of range-steps. For each range-step, a transmitter emits upwards at least one laser pulse, which is reflected downward by clouds onto a gated receiver. The gating interval of the receiver, relative to the emission instant, determines what rangestep is being explored. The gating interval is progressively shifted, to run through the range-steps. For each range-step, reflected laser pulses received during the gating intervals, if any, are integrated. Because the power attenuation of the reflected pulses is an approximately quadratic function of height, the relationship between the range-step value and the integrated signal is made approximately quadratic. In the lower part of the total range, this is done by progressively overlapping the conical beam patterns of transmitter and receiver, to create an overlap which increases quadratically with height. At least in the remaining upper part, an integration schedule is established, fixing for each range-step the number of pulses integrations performed before going onto the next range-step. The number of integrations performed per range step increases approximately quadratically as a function of range-step value or height. The beam-overlap expedient is used because of its simplicity, but is limited as to range. The integration-scheduling expedient is not limited as to range but cannot always be devised to span the transition between lower and upper parts of the total range. The two expedients in conjunction make it possible to span across the middle part of a large ceilometric range.</p> |
