Central California Ozone Study (CCOS) - Desert Research Institute

CCOS Field Operations Plan Version 2: 5/31/00
Alignment checks are performed on the sodar systems. The orientation of the antenna
array or individual component antennas will directly affect the accuracy of the calculated wind
directions. The orientation of the respective antenna arrays is checked using a tripod mounted
Brunton Pocket Transit. The measured orientation is then compared to the software settings in
the sodar. The criterion for acceptable orientation is ±2°. During the field audit, the compass
alignment to magnetic north is compared against solar observations and the magnetic declination
to verify the accuracy of the magnetic measurements.
The level of a phased sodar antenna array, or inclination angle of the horizontal
component antennas directly affects the calculations of the component speeds. The array level
(or inclination angle) is checked using a Pro SMARTLEVEL. The criterion for acceptable level
(or angles) in any direction is ±0.5°, consistent with EPA (1999).
4.4.3 Surface Meteorological Measurements
The system audits of the surface meteorological sensing systems consist of an inspection
of the site to assess proper siting of the instrument sensors, a review of the station check logs and
other site documentation, as well as an interview with the site operator concerning his or her
knowledge of the QIWP and applicable SOP sections. Sensor siting criteria for meteorological
sensors are specified in the EPA Quality Assurance Handbooks for Air Pollution Measurement
Systems, Volume IV (EPA, 1995). On-site forms and site logs are reviewed to check that the
documentation conforms to the specifications of the plan. The subjects that are addressed by the
system audits include:
Network design and siting
• network size and design
• sensor exposure
• review of station
Resources and facilities
• instruments and methods
• staff and facilities
• standards and traceability
Quality assurance and quality control
• status of quality assurance program
• audit participation
• precision and accuracy checks
Additionally, once the system audits of all sites are complete, the auditor checks for
possible differences in operation among the various sites.
4.4.4 Rawinsondes
The system audits of the rawinsonde operations consist of watching a launch and
comparing the procedures used to those specified in the SOP. Special attention is paid to ground
station and sonde initialization procedures, balloon inflation (with regard to proper accent rate),
Chapter 4: QUALITY ASSURANCE 4-11