Data Loggers Used in Microclimate Monitoring
Pacific Geodata (PGD) provides geographic information system (GIS) mapping and analysis services to vineyards, wineries, public agencies, and other organizations across the United States and abroad.
Matt Lamborn, owner of PGD and manager of his family's vineyard on Howell Mountain (Napa Valley's first appellation), combines his knowledge of vineyard management and GIS mapping and analysis to offer these services to others in the wine industry. In particular, PGD provides microclimate monitoring services to its vineyard and winery customers to help them understand the potential for frost and other growing conditions across their respective vineyard properties.
As part of a typical microclimate study, PGD uses Onset HOBO® data loggers to log both temperature and relative humidity levels. In one particular project, a total of 21 HOBO data loggers were deployed for a vineyard development study in rural Napa County. The data loggers were placed in a grid across a planned (but not yet planted) vineyard site in Napa Valley with two main goals: 1) to determine the extent of frost pressures throughout the rolling topography; and, 2) identify the range or growing degree day (GDD) values across the property and throughout the growing season.
The data loggers were mounted on 6-foot "T" posts using two large zip-ties. The logger housing was mounted with the cable pointing down and the communications window pointing up. This configuration, along with additional slack in the upper zip-tie, allowed for easy offloading using an Onset data shuttle. The shuttle is a handheld device that can be used in place of a laptop computer to offload, store, and transport logged data. All sensors were placed in gill-plated shields (see graphic below for detail).
In areas with high tractor and equipment operation, PGD fabricated PVC housings to protect the data collectors. The housing consisted of an 8" long section of 2" diameter PVC pipe with a fixed cap on one end and a slip cap on the other. PGD staff drilled the fixed cap and pulled the sensor and wire through, then mounted the housing to the T-post using extra large zip-ties. To offload the data logger, they would simply remove the slip cap and pull the logger out a few inches to connect the data shuttle.
Refer to the map (graphic 1) for a sample of the layout. The red points denote the HOBO data logger locations ("TR" are temp/RH units and "TT" are 2-channel temp units, each followed by a unique ID number). The number below the HOBO label is the actual Growing Degree Days (GDD) value for that sample point. The color gradations in the map are ranges of GDD values. They were created in GIS by interpolating the GDD value at each sample point across the site.
Measurements were taken every 15 minutes and the data was offloaded every 4 to 6 weeks and quickly reviewed to ensure data integrity. Onset's HOBOware® Pro graphing and analysis software package was used to review the data after each offload session, at which time PGD looked for anomalies or interesting trends that they might want to adjust for during the study period. The data were further analyzed and prepared for use in GIS by using Microsoft Excel.
By combining HOBOware, Microsoft Excel, and GIS, PGD came up with two main microclimate calculations at each data point throughout the planned vineyard site: 1) the number of frost hours, and 2) the number of growing degree days. The number of frost hours was calculated by totaling the number of hours where temperatures were sustained below 36ºF during a typical growing season. The 36ºF threshold was used because that is when the vineyard manager for this site would normally turn on the frost protection system. The GDD values were calculated using the average method, with 50ºF as the lower temperature threshold.
The data were used by PGD's client for three main purposes. First, in general terms, the data were used to simply identify and map the cooler and hotter areas of the site. Second, the data helped identify the areas receiving the most frost hours during the growing season. Frost information is critical because throughout many areas in Napa County groundwater scarcity is a serious concern. Identifying the most frost-prone areas allowed the vineyard manager to prioritize where frost sprinklers should be installed (i.e. in the coolest zones) and where it might be possible to get away with using fans (i.e. in the least frost-prone areas). Using this information could also significantly lower infrastructure costs to the winery (i.e. trenching and installing additional irrigation lines for the sprinkler system). Finally, GDD values were used to determine which wine grape varieties and rootstock/clone combinations would be most appropriate for the site's climate. In theory, using this information, coupled with slope, aspect, and soil maps of the site, would allow the vineyard manager and winemaker to grow vines that are most adapted to the site, lowering vine stress, environmental inputs, and management costs, while maximizing wine quality.
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