tailieunhanh - Atmospheric Acoustic Remote Sensing - Chapter 5

SODAR hệ thống và chất lượng tín hiệu Trong Chương 4, cơ sở lý thuyết đã được đưa ra để truyền của âm thanh trong các chùm tia hướng và nhận được tín hiệu tiếng vang. Các cơ sở để giải thích những tín hiệu về các thông số hỗn loạn và các thành phần tốc độ gió đã được thảo luận chi tiết. Đặc biệt, nó là điều hiển nhiên rằng mô hình chùm âm thanh hiếm khi đơn giản và rằng giải thích của các tín hiệu tiếng vang đòi hỏi kiến thức về thiết kế dụng cụ cảm. | 5 SODAR Systems and Signal Quality In Chapter 4 the theoretical basis was given for transmission of sound in directed beams and receiving echo signals. The basis for interpreting these signals in terms of turbulent parameters and wind speed components was discussed in detail. In particular it is evident that acoustic beam patterns are seldom simple and that interpretation of echo signals requires knowledge of the remote-sensing instrument design. In this chapter we discuss the details of actual designs so the connection can be made between hardware elements in Chapter 5 and the theoretical considerations of Chapter 4. TRANSDUCER AND ANTENNA COMBINATIONS Speakers and microphones Speakers are generally piezoelectric horn tweeters for higher frequency phased-array systems such as the Motorola KSN1005 or equivalent used in the AeroViron-ment 4000 or high-efficiency coil horn speakers such as the RCF 125 T similar to that used in the Metek SODAR RASS for lower frequency phased-array systems or high-power cone drivers such as the Altec Lansing 290-16L for single-speaker dish systems Fig. . Speakers are specified as having sensitivity of a particular intensity level Lị generally measured at a distance of 1 m for 1 W input electrical power I Li 10 logi0 10 12 Wm 2 for acoustic intensity I. For example the KSN1005 has an output of 94 dB for Vrms input voltage measured at a distance of 1 m or mW m-2. The Vrms reference gives 8 1 W into 8 H which is a common speaker resistance value. Since the conversion to acoustic power is an electrically lossy process equivalent to a resistance power output is proportional to vm and also the intensity is inversely proportional to the square of the distance so the intensity produced at distance z is 1 V Iz rm . z The maximum allowable input is 35 Vrms giving W m-2 at 1m distance. The frequency response for this tweeter is shown in Figure . The 3-dB point below the quoted 97 .