As a wine growing country, the United States is but an infant. Most
vineyards in France and other wine growing regions of Europe can trace
their origins back hundreds of years, well before the first vines were
planted in Napa Valley or Sonoma County. Because they have many
generations of experience backing them up, Old World vintners have
always maintained a slight advantage over the United States in the
production of high quality wines.
Probably in no area of winemaking has this been more evident than in the cultivation of the grapes. Since the Middle Ages, French wine producers have known that the quality of grapes a vineyard produces is heavily dependent on the health of the vines. Over the centuries, they have carefully studied their vineyards to uncover the slight variations of soil type, soil moisture, and microclimate that contribute to the grapes flavor. They then tailor their growing methods to suit the grapes being grown and the style of wine they are producing. By doing so they have achieved a far higher level of control over their harvest than their upstart U.S. competitors, who havent had the time to learn the lay of their land.
However, with the help of NASA technology, the wineries in California may now have a chance to catch up with their French counterparts. Using remote sensing, multi-spectral imagers mounted on planes, scientists have worked out a way to map the health of the vines across a vineyard in a matter of months instead of decades. Already, several of the larger wineries in Napa Valley, including the Mondavi winery, are using this information to rework their vineyards to get the best grapes. In the future these experiments may allow not only vintners but all crop farmers to know where to sow their crops to get the best results.
|Its all in the Grapes|
As anyone who has rushed into a liquor store looking for that
last-minute house warming gift knows, the range of quality and price
among wines can be overwhelming even when considering bottles from the
same winery. While these differences have much to do with the age of the
wine and the processes by which it is prepared, the distinction begins
with the type of grapes used.
Daniel Bosch, a senior technician at the Mondavi winery in Californias Napa Valley, spends most of his days managing grapevines. He explains that in order to age into a fine wine, grapes have to be just right when they are plucked from the vine. "We want the grapes to ripen at the correct size and not too early or too late," he says. For many wines, including the Cabernet Sauvignon, big, watery grapes will generally produce poor color and a thin taste. Small and unripened grapes on the other hand make for an acidic wine. In general, the berries need to be small, at their peak in ripeness, and full of flavor.
Bosch says that one of the keys to controlling the quality of the berries is to carefully balance the vigor of the vine with the number of grapes the vine produces. "Vigor" is agricultural speak for the health of a plant and is the result of the type and depth of soil a plant is in, the water it receives, and the sunlight it gets. Unlike most staple crops, vigor in grapevines is not necessarily a good thing. Highly vigorous grapevines, which are characterized by especially dense foliage, have more energy to grow fruit. If a relatively small crop is grown on a leafy vine, then the grapes will be big and watery. On the other hand, a stressed vine with less foliage does not have the energy to produce a big crop. If too many grapes are grown off of such a vine, the grapes will not ripen at all. "In instance where a vine is vigorous, you want to grow more grape-producing shoots to expend the vines energy. The opposite holds true for vines that are stressed," says Bosch.
Subdividing Vineyards Based on Vigor
Yet, even with this knowledge, demarcating the exact changes in vigor
to determine how many shoots to grow on the vine still isnt easy,
Bosch explains. Vineyards are rarely flat, and hills intersect and
follow many contours. The variations throughout a vineyard can be very
subtle and the dividing lines uneven. "Even if we go over the
vineyard row by row and taste the grapes and analyze the vines, it can
be pretty confusing," Bosch says. "The variability isnt
always in a straight line."
For centuries, the French have managed to separate their vineyards by vigor and then manage each section to achieve an extremely high level of control over their grapes and quality of wine. Bosch explains the French reached this plateau by carefully studying the soil composition and topography of their wine-growing regions over many years. Some also monitor the leaves as they turn every fall. Vines with more vigor hold onto their leaves for much longer than vines under stress. Watching a hillside turn can give them a good idea of how to prune the crops from year to year.
Bosch points out that the problem with these techniques is that they take years and years to implement and require generations of experience, whereas the extensive wineries of the Napa Valley were only planted within the past 50 years. While the early Napa vintners chose a good area to grow grapes, they did not go to great lengths to subdivide the vineyard in terms of how vigorous the vines would grow. Instead they subdivided the vineyards based on road access and plot size. "When we started, we simply didnt understand how subtle the variations could be from vine to vine," says Bosch. As a result they never have achieved the level of control over the grapes they harvest that the French have.
Until recently this lack of control didnt matter so much, since the demand for premium wines from Napa Valley was not very high. But along with a growing reputation, a good economy, and a refinement of the American palate, the demand for reserve wines grew substantially in the early 1990s and drove the price up from around $35 per bottle for the most expensive wines, to well over $100. Several years ago, the wineries began to look for ways to detect the health of the vines and subdivide the vineyards by vigor, so that they could create larger stocks of reserve wines. They needed a method that wouldnt require decades to implement.
|Using Remote Sensing to Determine Vine Vigor|
The answer to the winery's problem came from a seemingly unlikely
source. During the early 1990s, most of the wineries in Napa Valley were
struck by the worst insect epidemic in their 40-year wine growing
history. Tiny, aphid-like insects, known as phylloxera, swept across
Northern California infecting grapevine after grapevine. The insects
would feed on the vines roots and in doing so leave them open to
fungal infections that would kill them in two or three growing seasons.
Under the direction of remote sensing researcher Lee Johnson, scientists at NASA Ames Research Center became involved with the Mondavi winery to find ways to predict the devastation of the crops. They set up a series of trials wherein they used multi-spectral digital cameras mounted on aircraft to detect the insects by measuring the density of foliage across the vineyard. The studies helped the vineyards monitor the spread of the insects so that they would know precisely when and where they had to pull the existing grapevines and replant with phylloxera resistant vines. In the midst of this project, those researchers involved realized that this same technology could be used to separate vines of varying vigor.
In these phylloxera experiments, we saw with the multi-spectral imaging data that the amount of foliage on the vines is directly related to their stress levels, says Johnson. In phylloxera infested plants, a lack of foliageeither fewer leaves or smaller leavesusually means the plant has become stressed by the insects and is dying. The researchers reasoned that differing amounts of foliage in crops that are not infested may be a good indicator of vine vigor. Specifically, more vigorous plants will have more foliage.
NASA and the Mondavi winery teamed up again in an experiment named CRUSH (Canopy Remote sensing for Uniformly Segmented Harvest) to test whether remote sensing could delineate the plants by their vigor and ultimately by the quality and characteristics of the grapes the vines produce. Johnson explains that the multi-spectral imager they used is essentially a very precise digital camera. Unlike a hand-held camera with film, this imager has several types of digital photoreceptors on it that record very specific wavelengths (colors) of light. The ADAR System 5500 the Ames scientists employed was developed with the assistance of NASAs Commercial Remote Sensing Program and has four different sensors. One detects only the blue light, one detects only the green light, one the red light, and one the near-infrared light. The data the sensors receive are fed into a computer where images can be produced of each band or combinations of the bands (Johnson et al., 1998).
For the CRUSH project, the scientists mounted this imager on a prop airplane, which was then flown 15,000 feet above the vineyard. To determine the thickness of foliage across a vineyard, they trained the imager on the amount and colors of sunlight reflected off the leaves (Johnson et al., 1998). As can be seen through a prism, many different wavelengths make up the spectrum of sunlight. When sunlight strikes objects, certain parts of this spectrum are absorbed and other parts are reflected, and some heat is emitted. In plant leaves, chlorophyll absorbs red light and other visible wavelengths from the sun for use in photosynthesis. The cell structure of the leaves on the other hand reflects near infrared light. The more foliage a plant has, the more these types of light are affected.
Since the imager measures the intensity of infrared and red light coming off the vineyard, the scientists simply gathered the data the instrument recorded on its flight and compared the intensity of the two types of light across the vineyard. In general, where the difference between infrared and red light was at a high value, then the vines had more foliage and were probably more vigorous. Where the imager recorded low values of this difference, the vegetation was less dense and the vines were probably less vigorous. All of these imaging data were then fed into a Geographic Information System, computer software that essentially matches up the raw images with the landmarks and topography on the ground. The result was a complete map of the vineyard showing general areas where the vines were vigorous, and areas where the vines were stressed.
The remote sensing gave us a good rough outline of where the
high, medium and low-vigor plants were, says Johnson. Technicians
at the winery then went around to these areas and tasted the grapes and
ran a number of chemical and water tests to see if the aircraft
measurements were correct. After some trial and error, they were able
to get a full picture of grapevine vigor across many acres of the
Its amazing to see how small a change in slope, for instance can affect the quality of the grapes. We found that an increase of a few inches in elevation on a hillside will make a difference," says Bosch. Over the past two years, the winery has begun to micromanage the vineyard based on these subtle differences in vigor. Given the vigor of the vine, Bosch explains they can change the amount of shoots grown by first pruning for the correct number in the fall and then increasing or decreasing the amount of irrigation water the vine receives as it grows. Though it still takes some time to get results, every acre of the vineyard that they can transform into reserve wine quality grapes increases their revenue by $800 per year. Of course in some areas theyve found that the vigor is the same throughout and there is not much they can do.
Beyond providing the wineries with a bigger profit, the remote sensing images have educated the technicians in how to manage a vineyard. Seeing all of it at once gives us more experience and the ability to recognize the patterns fairly quickly, says Bosch. Only after a few years of using the remote sensing devices, he boasts he is getting to the point where he can spot the variation on his own without the imagery. In the fall, he can now clearly see the order in which the leaves turn. Within the span of a few years, theyve essentially been able to do what took the French decades to accomplish. This is a real revolution in how we are able to manage our vineyards, says Bosch.
Successful Tests Lead to Ongoing Research
Ultimately Johnson would like to know how vigorous vines on a patch of land will be before they even plant the first seedling. His team is working with several models developed jointly by scientists at NASA and the University of Montana that may be able to do just that. Given the topography and soil type of a patch of land, these models should simulate how various crops will grow on uncultivated land. In this way wineries could design a vineyard based on plant vigor from the start, says Johnson. Experiments like the ones they performed at the Mondavi winery allow the scientists to refine the model. By first testing the model on regions that are already planted, they can get estimates on how the model works and then adjust it to work on areas without plants.
In the long run, the goal of the Ames team is not only to improve the quality of wine in California, but also to gain a better understanding of how to use remote sensing systems and irrigation methods to deal with crop stress. Farmers who raise soybean and corn crops do not want their plants to be stressed at all. By understanding what causes stress in wineries, future agriculturists may be able to look at any crop and tell farmers the best way to irrigate and farm using the least possible resources. The study is a nice example of a NASA-funded science project that has scientific merit as well as economic benefits, says Johnson.