WMOD00296 (2) - Laserfiche WebLink

Home Browse Search

7!t II seeding. In addition, an EG&G Cessna 180 was used for some aircraft seed- ing and for line source pyrotechnic releases for diffusion tests" The Queen Air was almost always operated IFR (instFument flight rules) and the Cl80 always VFR. The C180 was based in Craig during March so any truly oro- graphic cloud formations could be seeded by operating VFR out of Craig and moving up under the cloud base and in as close to the edge as possible. Initially it was planned to make the seeding runs by navigating off of the available navigational aids in the area. It soon became apparent that radar tracking of the seeding aircraft would be necessary to adequately define the exact position of seeding releases. It was undertaken to track the aircraft and use the Ajax plotting boards for record. This worked fairly-well once the aircraft was located and the tracking radar locked on. If this were to be done in the future, the procedure would be greatly simplified if the PPI (plan position indicator) presentation from an acquisition radar were avail- able. The pilots could not report position rapidly enough or accurately enough to permit rapid lock-on to the aircraft, so the search procedure re- sembled looking for a needle in a haystack. y A high quality communications system is a definite requirement for this type of operation if the aircraft is to be vectored from the ground and the pyro- technic seeding fired on command from the ground. A pilot I s full time is required to maintain required contacts with A TC (air traffic control) center. A second pilot is needed to communicate with the radar control. These two communication channels should be completely separate so that the communi- cations with center do not interfere with the communications with radar con- trol and vice versa. Also, a special airspace clearance with center is desirable, so that plume tracking can be done at any level dictated by the results as the test progresses. Under the usual clearance, it is difficult to change altitude for plume tracking and other desired measurements. 2. 4 Radiosonde Releases From the beginning of the project, the importance of on- site radiosonde data was realized. During the first season of seeding experiments a 403 MHZ radiosonde system was used, but it was not entirely satisfactory. The next season, a 1680 MHZ system was procured and installed at the Mt. Harris site. This system was built around a standard GMD-1 receiver and used standard ESSA 1680 MHZ sondes. The wind determination and direction finding function was performed by the 3 cm tracking portion of the Nike Ajax radar. This equipment performed reasonably well over three winter seasons and a large body of radiosonde data for true orographic flow has been collected. 2. 5 Radar Observations 2. 5. 1 Introduction : 19