EVERYTHING YOU WANTED TO KNOW ABOUT THE ELECTROMAGNETIC SPECTRUM

... but were afraid to ask!

A generalized composition of our Sun's radiation.
The vast majority of the electromagnetic radiation emitted by our Sun is in the form of infrared, visible-light, and ultraviolet. Click diagram to expand.

Greetings! This is the first in a four-part series on the use of cutting-edge research, digital imaging technology, autonomous aeronautics,  geographic information systems, and positioning technology as a force-multiplier for the talents of the modern vineyard manager.

This week’s installment is a synopsis of the nature of the electromagnetic spectrum – a knowledge primer to use as a springboard to better understand the phenomena making reliable observation of plant health that beyond the capability of the unaided human eye a reality. 
 
Many vineyard management and other wine industry professionals have encountered references to the electromagnetic spectrum, or ES. 
Within the viticulture space, you may be aware of the use of specialized cameras to analyze light reflected off foliage to determine plant health. In winemaking, many of you are familiar with spectrophotometry, involving light of certain color ranges being shone through a sample of wine, indicating the presence and concentration of certain compounds.  
 
Both of these techniques make use of the electromagnetic spectrum’s interaction with matter that we want to study and gain insight into. Much like the microscope and telescope before them, multispectral cameras and spectrophotometers extend our ability to understand parts of our world that are invisible to the naked eye – creating a kind of extrasensory insight. 
 
The electromagnetic spectrum, as a topic of discussion, is infinitely complex. Minds no lesser than that of Albert Einstein's grappled with its finer points. However, this blog post will bypass any treatment of arcane particle physics – instead focusing on the practical dimensions of the subject.  
 
The electromagnetic spectrum is all around us - without it, life as we know it could not exist; to wit, the plants at the base of the food chain rely directly on the ES as the energy source for photosynthesis. 
Electromagnetic radiation is generated by stars like our sun, yet we also create it with our technology – radio stations, toasters, light bulbs, X-ray machines, and the detonation of atomic bombs all emit electromagnetic waves that are part of the ES. Even our bodies contribute, in the form of radiant heat. 
 
Electromagnetic radiation takes the form of a continuous stream of tiny, energy-containing particles called photons, that move at the speed of light. These photons oscillate, or move up and down vertically, along their horizontal path. This results in the stream of photons developing a wave pattern. The more energy these photons contain, the more rapid their oscillation, resulting in greater frequency and a shorter wavelength.   Here is a useful simplification, in the form of a pseudo-equation:

Higher Frequency = Shorter Wavelength = More Energy.

The portions of the electromagnetic spectrum are classified by wavelength – with very long waves used in radio communications, mid-length waves to run our microwave ovens and infrared heaters, and very short waves running our CAT-scan machines. 
 
What does this all have to do with the vineyard, you ask? Lots! But first, we must put the vineyard in context. All portions of the ES are either helpful or harmful to life on earth, but the most fundamental portion of the spectrum to life as we know it is a tiny slice in the range with wavelengths between ½ millimeter and 1 / 2,500th of a millimeter. Not all of this range is visible to the human eye, which has evolved to detect only a “Goldilocks zone” of wavelengths carrying an amount of energy that is “just right”. We perceive this range of wavelengths as the familiar ROYGBIV color spectrum – also known as visible light. We have evolved to perceive this range of electromagnetic radiation due to the heat of the surface of our Sun - about 9,980 degrees Fahrenheit - that emits 95% of radiation that strikes the surface of the earth in wavelengths that we see as visible light, and feel as infrared radiation. 
Infrared radiation, which occupies the ½ millimeter to 7/10,000th of a millimeter range, is sometimes referred to as “light”. This is technically incorrect, as it is invisible to our eyesight (see diagram) - we sense this wavelength range as radiant heat. 
 
So, on to the vineyard! The photosynthetic foliage of plants has selectively evolved pigments that absorb wavelengths of solar energy in the range we perceive as red and blue, due to their greater suitability for driving the photosynthetic process - and reflect the energy waves of lengths we perceive as green. These reflected “green-length” waves make their way to our eyes and

 
  A generalization of photosynthetic foliage's interaction with solar electromagnetic radiation.   Wavelengths in the  violet ,  blue ,  orange , and  red  ranges are strongly  absorbed  by pigments in plant tissue, where they are a fundamental innput to photosynthesis, flowering, and leaf orientation. Wavelengths in the  green ,  yellow , and  infrared  ranges is  reflected  and/or  transmitted , thus detectable to sensors such as a multispectral camera (or the human eye, in the case of green and yellow only.)

 A generalization of photosynthetic foliage's interaction with solar electromagnetic radiation.
Wavelengths in the violet, blueorange, and red ranges are strongly absorbed by pigments in plant tissue, where they are a fundamental innput to photosynthesis, flowering, and leaf orientation.
Wavelengths in the greenyellow, and infrared ranges is reflected and/or transmitted, thus detectable to sensors such as a multispectral camera (or the human eye, in the case of green and yellow only.)

cause us to perceive the familiar color of healthy foliage.  
Infrared radiation that is carried by waves just longer than that of red light – yet not short enough to be visible -  are known as near-infrared. Like green-length waves, they are not absorbed by any pigments present in plant foliage, so they are reflected or transmitted (pass through the mesophyll cells to the ground below). The healthier, more turgid, and denser the plant foliage, the greater the proportion of near-infrared radiation that is reflected rather than transmitted. Thus, to the observer above the plant (read: us) reflection of more infrared and green, and less red and yellow, morereflected indicates more vigorous foliage.  
 
But there are two problems here. The first is obvious: our eyes cannot detect this near-infrared radiation. The second is more complex: what is the reference point constituting strong or weak reflectance? Fortunately, scientific research and technological advancement has been directed at these problems over the past century or so, and we are currently refining and researching the discoveries advanced by full-spectrum photography to drive incredible insights into plant health.  

A general depiction of how photosynthetic foliage interacts with wavelengths in the red, yellow, green, and infrared ranges.    - A -  Foliage of plants under stress  transmits   more IR ,  reflects   less green & IR  and  more red   & yellow .  - B -  Under relatively balanced stress conditions, foliage  absorbs   red ,  reflects   green ,  transmits   less   and   reflects   more IR,  and  transmits   most yellow .  - C -  Under healthy, vigorous conditions, foliage  strongly   absorbs   red,  and  strongly reflects   green and IR . Yellow is  almost completely   transmitted  .

A general depiction of how photosynthetic foliage interacts with wavelengths in the red, yellow, green, and infrared ranges.
- A - Foliage of plants under stress transmits more IR, reflects less green & IR and more red & yellow.
- B - Under relatively balanced stress conditions, foliage absorbs redreflects green, transmits less and reflects more IR, and transmits most yellow.
- C - Under healthy, vigorous conditions, foliage strongly absorbs red, and strongly reflects green and IR. Yellow is almost completely transmitted .

The first problem began to be solved sometime in the first half of the 20th century with the development of film sensitive to infrared radiation. The second problem involves the development of algorithms. Healthy plants of a given species will reflect green light in a very tight and predicable wavelength range – visible in the very homogenous green color of a vineyard, for example. As a plant’s health deteriorates, the range of wavelengths reflected by its foliage begins to shift from green to yellow – a familiar sight. In addition, the red light that would be absorbed by the plant under healthy conditions begins to be reflected. This is the cause of the familiar yellow/brown appearance of an unhealthy plant.  But before this becomes visible to the human eye, the level of reflectance of infrared radiation begins to drop. Thus the relationship between infrared, red, and green reflectance can be expressed as a ratio. Changes in this ratio are a signal that serves as a very reliable early warning to changes in plant health before they become visible. 
 
Stay tuned for next week’s installment – how specialized multispectral cameras can be put to use in reliably recording this change in ratio!         

2016/17 Record Rainfall - PRIMED for vigor

A common sight in early 2017. Finally. Napa County, April 12th, 2017.

A common sight in early 2017. Finally. Napa County, April 12th, 2017.

WITH measurements starting October 1, 2016, the 2016/17 winter rains have been characterized by some gangbusters events. As reported by the LA Times, a 122-year precipitation record has just been set in the northern Sierra - edging out the 1982-83 season - and the breaking of more records appears imminent in other areas of the state with a wet beginning to this week.
 
As per usual, the rainfall totals have resembled a crazy-quilt up and down the West Coast. Sonoma and Napa Counties (Map 1) , western SLO (Map 2), and Santa Cruz / Monterey (Map 3), took it on the head - with totals exceeding 200 and even 300% of their long-term precipitation averages.

Map 1: SF and the North Bay.

Map 1: SF and the North Bay.

Map 2: SLO, Santa Barbara, and southern Monterey Counties.

Map 2: SLO, Santa Barbara, and southern Monterey Counties.

Map 3: Santa Cruz and northern Monterey Counties.

Map 3: Santa Cruz and northern Monterey Counties.

Meanwhile, the Pacific Northwest had a healthy rain year (Map 4), with much of the region receiving 110 to 130%+ of the normal amounts, and Santa Barbara County experiencing a relatively normal precipitation year (Map 2). All maps courtesy of the California-Nevada and Northwest River Forecast Centers.

Map 4: The Pacific Northwest.

Map 4: The Pacific Northwest.

The soggy season saw a lot of growers delaying pruning until conditions grew sufficiently dry to avoid encouraging the spread of disease, only to face the challenges involved in getting pruning crews into flooded blocks. Fortunately, many of the precipitation events of the season were short and intense, often allowing standing water to drain off in a matter of days.

This year's bud-break has occurred at a relatively "normal" time in many growing regions, at least compared to the last few drought years, and vineyard managers are anticipating the likely effects on the grapes going into the 2017 vintage.

Vineyard blocks featuring efficient drainage are expected to undergo a rapid but relatively straightforward start, with general tendency toward abundant water availability in the root zone, improved soil structure, and lowered salinity levels thanks to the flushing of drought-affected soils. To maintain vine balance and promote timely cluster ripening, a close eye will have to be trained on the canopy, which is likely to display heightened vigor.

For vineyard blocks that experienced extended periods of standing water this winter, there are added considerations. Whether the pooling was caused by large amounts of runoff from higher blocks nearby or clay soils contributing to poor drainage, vines in these areas may show marked variations in vigor as the growing season gets underway.

In poorly drained soils, though the vineyard floor appears dry, supersaturated conditions may still exist in the root zone. In this case, vines can exhibit signs of "spring sickness" or "wet feet" caused by hypoxic conditions in the soil environment. When these conditions are short-lived, the effect on the vine is rarely fatal, but partial root death may slow early-season growth.

Some of these areas may actually see an increase in salinity, as the water that was pooled there likely contained high concentrations of salts leached from other, better-drained areas.

Increased salinity can also come from below, particularly where perched groundwater is present. Rising water tables can dissolve salts built up through irrigation in dry years and deposit them higher up in the soil profile as water levels recede, possibly in the root zone.

Under both hypoxic and saline soil conditions, the vines' ability to regulate sodium and chloride ion concentrations in their roots is decreased; interfering with the normal uptake of essential nutrients such as nitrogen, phosphorus, and calcium.

Thus, some vineyard blocks that were partially affected by flooding in the past months may exhibit higher variation in vigor than has been seen in recent years, potentially bringing added complication to the all-important task of canopy management.

Hawk Aerial provides highly accurate vigor mapping by collecting data on the proportion of specific wavelengths of light reflected by vine foliage - which differs significantly with the intensity of photosynthesis occurring in the plant at the time of image capture. We then use this information to create maps displaying explicit visual differences between areas of high vigor and areas of low vigor - a very rapid way to gather crucial information informing canopy management strategy.

In contrast to the vast majority of NDVI-derived maps on the market today, our data products undergo processing that removes interference generated by ambient light quality and reflectance from cover crop and other non-vine vegetation - showing you the vigor levels of your vines, period. Vigor mapping not only gives your vineyard management professionals a roadmap from which to start in their short-term planning, but also creates a record over time that can shed light on areas of the vineyard featuring chronically high or low vigor. This can drive decisions on more involved intervention, such as soil amendment, installation of drainage infrastructure, et cetera. 

Our Calibrated Enhanced Vegetation Index (CEVI) package provides growers and vineyard managers with three ultra-high-resolution, scale-accurate, georeferenced maps per imaging mission, details of which can be found by clicking the buttons below. Contact us to book an imaging mission today, and get a head start on your canopy management planning!

     

Hawk Aerial's analytical map benefits featured in The Grapevine magazine

Citing Hawk Aerial CEO Kevin Gould, The Grapevine magazine notes "new developments in vineyard map technology have helped eliminate inaccuracies that existed in older methods."  The article goes on to explain the importance of switching from NDVI to EVI (Enhanced Vegetation Index) maps, and discusses the technology advantages of using drones over airplanes or satellites.  Read the full article by clicking HERE.