Robert A. Baxter, Certified Consulting Meteorologist

Professional Specialties

Audit Methods -- Acoustic Pulse Transponder

Acoustic Pulse Transponder electronics
APT Electronics Initial guidance on the performance auditing of sodars specified multiple comparisons with an independent means of collecting data in the altitude range of the sodar. The standard technique was to use a tethersonde, which was time consuming, expensive and logistically difficult at some sites. In the early 1990s I developed an instrument that simulated the atmospheric reflections of a sodar pulse by accurately generating time and frequency shifted tones mimicking the Doppler shifted echoes for which the sodar listens. Since the development of the Acoustic Pulse Transponder (APT), the USEPA has incorporated the use of such an instrument in the guidance for performance auditing sodars (USEPA, 2000). Summarized below is a description of the APT.

Selected papers on the development and use of the APT are shown below. Additional details on the papers can be found on my publications page.

Selected publications detailing the Acoustic Pulse Transponder include:

  • Quality Assurance of Data Produced from Sodars -- Application of a New Instrument for Field Performance Auditing, 1995
  • Performance Auditing of Sodars Under the New USEPA Guidance -- Applications of a New Instrument to Quantitatively Assess Sodar Performance, 1995
  • Development of a Universal Acoustic Pulse Transponding System for Performance Auditing Sodars, 1994
  • Performance of Sodar Audits Under the New USEPA Guidance, 1994
Block diagram of the APT
APT block diagram Quality Assurance performance audits have been conducted on a number of sodars using the APT. The sodars have included those manufactured by AeroVironment (models 2000, 3000 and 4000), Metek (MODOS), Radian (models 600, 600PA and 300), Remtech (P0, PA2) and several types of NOAA/ETL sodars. While the APT best simulates the single frequency pulse return, it has been programmed and used successfully for auditing a five-frequency Remtech PA2 sodar. The versatility of the instrument allows the simulation of vertically consistent wind speeds and wind directions, or a series of wind shears in both speed and direction.  Two different configurations allow the auditing of either phased array or multi-axis antenna sodars. 

The APT software runs on a laptop computer in a DOS environment to maximize the efficiency of the computer timing. It can also operate in some Windows environments (9x and XP), providing the processor speed is adequate and the communications port interrupts don't interfere with the APT communications.  

Transponder over PA2  Transponder in front of AV4000
Transponder over a Remtech PA2 array and in front of an AeroVironment 4000 array

Return to HOME   BACK to Audit Methods
Copyright © 2002, Robert A. Baxter