Software interprets satellite images for grape growers ByBob Johnson
the program, which is available online: irrisat-cloud.appspot.com. The first case was a Central Valley table grapevineyardwith inconsistent andpoor growth early this spring. The satellite data let Battany see that vegetationinthevineyarddeclinedquickly shortly after the 2020 harvest, which led to the theory that an early irrigation cut- off had caused diminished carbohydrate buildup last offseason, leading to poor growth early this year. Irrisat softwaremadeitpossibletoquick- ly generate a series of one-year graphs of the vegetation, crop coefficient andwater use in that vineyard that showed therehad beena change in irrigationpractices. “They shifted their management from continuing irrigation after harvest to cut- ting it off earlier, which resulted in slower growth early this year,” Battany said. “The three years of charts show they cut off wa- ter pretty early last year, and it resulted in less carbohydrate accumulation.” In another case study, a vineyard showed a five-year pattern of declining foliage after spring growth. “The NDVI photographs show vegeta- tion in May, but areas start to decline in June, and in July we see the same thing progressing, but it is gettingmore severe,” Battany said. “Lookingbackover years, we can see it is probably not a disease but in-
stead a problemof irrigation distribution uniformity that is resulting inweak areas.” He said historical satellite vegetation photographsmade it possible to track the rise and decline of a Central Coast wine- grape vineyard planted in 1999 that later developed severe trunk disease. “The NDVI data goes up from2000 un- til 2015, except during a drought,” Battany said. “After 2015, you can track the rapid decline fromtrunk diseases.” The historical photographs also show a quite different growth pattern in anoth- er Central Coast winegrape vineyard, in which the farmer moved aggressively to combat trunk disease. In this vineyard, the grower saw the symptoms of the disease, aggressively cut back the vines at a significant loss of short-term yield, but then, the historical photos reveal, they enjoyeda rapid return to vigor. In a Napa Valley study, the imagery made it possible to see the impact differ- ent cover crop termination dates in wet and dry years had on the rate of early vine growth the next spring. “You can test the relationship be- tween how long you let your cover crop grow and the later growth of the vines,” Battany said. There are limits to the accuracy of the satellitephotos, however, andhe said they
can interfere with accurate diagnoses if those limits aren’t accounted for. One potential source of inaccuracy is that satellite photographs do not edit out areas such as roads that would distort the average vegetation of a vineyard, block or 10meter-squared area. Another shortfall is that clouds can make it impossible for satellite-based cameras to see the vineyards, resulting in a blank spot in the data. The Irrisat soft- ware lets the user choose to edit these blank spots out of the charts and replace them with values that approximate the level of vegetation that would have been photographed, had the clouds not gotten in the way. In another case, a farmer put plastic on Central Valley table grape vines to pro- tect them from heat, but satellite NDVI cameras saw the plastic as cloud cover. Although this left a hole in the vegetative growth data during the period when the plastic was on, the imagery still provided potentially valuable historical informa- tion about management of the vineyard, Battany said. “You can’t get NDVI data, but you have a record of when plastic was put on, how long it stayed on, and the impact it had on growth after it was removed,” he said. ( Bo b J o hn s o n i s a r e p o r t e r i n Sacramento. He may be contacted at bjohn11135@gmail.com.)
Vineyard managers may find satellite imagery amore useful tool, as vegetation photographs are taken more frequently at higher resolution and farmer-friendly softwaremakes it easier to distill practical implications of the data. The satellites Sentinel-2A and -2B take pictures with 10 meter resolution every fivedays,while theolder Landsat satellites still offer 30meter resolution images every eight days. And a new software program designed specifically for farmers makes it easier for experienced hands to use this datatoanalyzechangingconditionswithin a vineyard. “The Irrisat software programwas de- signed by farmers and is very practical,” saidMarkBattany,UniversityofCalifornia CooperativeExtensionviticulture farmad- visor inSanLuisObispoandSantaBarbara counties. “It is mainly intended as an irri- gation tool.” Battanymade his remarks as he offered a virtual primer on using satellite-based Normalized Difference Vegetation Index informationtoanalyzevineyardconditions. “Irrisat is theprogramIuse themost,”he said. “It even converts NDVI data to crop coefficients that can be used in combina- tionwith local weather data.” Battany went through a series of case studies showing the analytical power of
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