Environmental Engineering Reference
In-Depth Information
7.2 DATA RETRIEVAL
The selection of a data transfer and handling process (manual or remote) depends on
the characteristics of the site and requirements of the monitoring program. In general,
remote data retrieval is preferred since it usually involves less staff time and travel
expense. However, some sites may not have reliable cellular phone service, and other
remote connection options can be expensive. In choosing a method, the following
points should be considered:
labor costs and availability;
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travel time and expense;
•
year-round site accessibility;
•
availability of cellular phone service;
•
communication equipment costs and power needs;
•
support systems required (e.g., computers, modems, analysis and presentation
software).
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7.3 DATA RETRIEVAL FREQUENCY
Whether data are retrieved manually or remotely, frequent retrieval and prompt review
are key to achieving high data quality and low losses. A schedule of regular site data
transfers, or downloads, should be followed. The maximum recommended interval is
2 weeks. With remote data transfer, the size of the data sets to be transmitted is an
important consideration. For reliable transfers, the files should be as small as possible.
A weekly schedule may suffice, but a shorter interval, such as every 1-3 days, may
be better.
Situations may arise that warrant unscheduled transfers. For example, if sensor
irregularities are discovered when the data are reviewed, a follow-up transfer may
be called for to see if the problem is persisting. Reports of icing or severe weather
near the site could be the cause for making an unscheduled retrieval to make sure the
sensors are still working properly. Of course, whenever problems are suspected, a field
crew should be dispatched as soon as possible to inspect the tower and instruments.
7.4 DATA PROTECTION AND STORAGE
The following sections offer guidance to minimize the risk of data loss and corruption.
7.4.1 Data Logger
To ensure data are protected while stored in the data logger, proper installation pro-
cedures should be followed, including grounding all equipment and using spark gaps.
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