Satellite data has become an integral part of modern agricultural management to keep track of crop progress. Some satellite data, however, also can foretell how a crop will perform in the future, offering valuable insights to a wide range of industry players.
NDVI is probably the most important of the satellite data. By reading infrared light waves reflected from plants, NDVI can signal stresses to plant health, such as oncoming drought, as much as two weeks before problems are visible to the naked eye. Many agricultural industry participants can benefit from such advance alerts. Farmers can increase irrigation or add crop protection to forestall a pest infestation. And physical traders, processors, and food and beverage companies could seek out alternative supplies, or hedge their positions.
NDVI also can reveal positive indications about a crop, providing a heads-up to market participants, logistics companies, and others to prepare for a big harvest. Another type of satellite data, called evapotranspiration (ET), also sends early-warning signals about plants, based on measures of moisture evaporation and transpiration. But ET is available only on a monthly basis, much less frequent than the eight-day reports on NDVI.
NDVI is the key input to Gro’s machine-learning-based yield models. It plays a decisive role in Gro’s yield forecasts for corn in the US and Argentina, soybeans in the US, and wheat in countries including Ukraine, Russia, India, and the US.
In this Weekly Insight, we explain the science behind NDVI and the impact it has on Gro’s robust yield models. We also examine cases when awareness of NDVI signals could be put to valuable use by industry and government officials.
Early space exploration quickly led to atmospheric and meteorological studies. NASA in 1972 launched the Earth Resources Technology Satellite, the forerunner to Landsat, the world’s longest-running satellite imagery program. This first satellite was able to distinguish between visible red and near-infrared reflectance bands, which allowed it to identify vegetation, soil, water, and other features.
Light from the sun is present as visible light (reds, greens, and blues) and light not visible to our eyes (infrared and ultraviolet). These can be absorbed, transmitted, or reflected by an object. In healthy plants, most of the visible light is absorbed for use in photosynthesis, and much of the near-infrared radiation (NIR) is reflected. However, if the plant is stressed, because of dehydration, for instance, it reflects less NIR and absorbs less light in the visible spectrum, specifically in the red portion, since the plant is not using photosynthesis as efficiently.
Using these assumptions, researchers formulated the so-called normalized difference vegetation index, or NDVI. The equation looks like this:
NDVI = (NIR - Red)/(NIR + Red)
Simply put, NDVI measures plant greenness, a direct measurement of chlorophyll content and photosynthetic activity, which is a basic but reliable way to gauge plant health and biomass, or yield. Using the simple equation above, which returns values between 0 and 1, a higher value represents a healthier plant.
Numerous satellites capture light at these wavelengths. They differ by factors such as pixel size, or how much area is covered in a single image, and by how often the satellite returns to the same region, known as revisit time. Gro chose to use the MODIS sensor aboard the TERRA and AQUA satellite, which has a nominal spatial resolution of 250 meters by 250 meters. It also has a daily revisit time, which is aggregated to eight- and 16-day products in order to allow for cloud cover. The MODIS sensor also has an archive going back to 2000, which gives users the ability to model long-term trends.
Traditional survey-based yield modeling is slowly being supplanted by remote-sensing techniques as satellite technology continues to improve. Changes in crop condition can be detected more quickly using NDVI, which reads near-infrared light waves. Crop stress from pests, diseases, drought, flooding, and other factors won’t immediately be picked up in the visible-light spectrum, but will be reflected in the NIR spectrum.
Simply looking at a map of NDVI readings, however, can often be misleading, partly because the data doesn’t distinguish between planted crops and non-target vegetation, such as surrounding trees. Identifying the exact areas where crops are growing, called crop masking, is a critical first step, and NDVI plays an important role in this process, as well.
Yield models contain a variety of climate inputs such as temperature and precipitation that provide valuable insights about growing conditions. Other variables, like evapotranspiration, reveal information about the condition of the crop and soil moisture. But NDVI is the only variable, in addition to latitude and longitude, that is included in every one of Gro’s yield models. It is also the only yield model variable that directly measures plant activity, in this case photosynthesis, which ultimately determines yield. Other variables in our yield models act as proxies for plant health, but don’t directly measure production of biomass.
NDVI is most effective beginning in the pre-peak season of crop growth and continuing through harvest. Earlier in the season, when most crops are just starting to show shoots, NDVI doesn’t provide much useful information because it isn’t reading as much surface area.
To be sure, NDVI also is less effective with certain crops. In production of ratoon crops like sugarcane, for example, large fields of shoots are cut and harvested over four- to 12-month periods while the roots are left to regenerate. This practice results in significant spatial and temporal variation in growth over sugarcane acreage, which presents a challenge to monitoring yield using NDVI.
A good example of the usefulness of satellite imagery to identify crop risks was during the devastating Mexican drought of 2011-12. Evapotranspiration readings and other indices were signaling severely dry conditions in the spring of 2011. Although many farmers had already committed to ambitious plans for the year, some still had time to alter decisions. Meanwhile, the NDVI anomaly index—which runs from -1 to +1 and compares historical, or normal, conditions with the current condition—was below a neutral reading of 0, forecasting weak yields. Processors and consumers could have hedged against higher prices but, unaware of the alarming satellite signals, generally did not.
The fallout for Mexico’s agricultural sector was disastrous. Corn yields in Mexico dropped 11% between 2010 and 2011 and producer prices jumped 45%. Imports rose to meet demand for the country’s most consumed grain.
NDVI also can send positive signals. After a dismal 2012 harvest, producers in the US Corn Belt were hoping for an upbeat 2013. While initial forecasts looked promising, the USDA, in its monthly WASDE report, gradually reduced yield estimates each month from May through August. Finally, in November, the USDA sharply raised its yield forecast, more than retracing its reduced estimates since the previous spring. The USDA explained that “cooler-than-normal summer temperatures” had offset dryness across the Corn Belt.
NDVI readings, however, were signaling throughout the 2013 growing season that the crop was in better shape than the USDA estimated. NDVI anomaly measurements for the Corn Belt increased weekly from -0.38 in mid-June to 0.26 in the last week of August. The upshot: Final 2013 yield was 158.1 bushels per acre, a 28% jump from the previous year.
Similarly, Brazil’s record soybean crop in 2018 was anticipated by satellite data. For 17 straight weeks, between the end of September 2018 and the end of January 2019, NDVI was the highest it had been for the previous 10 years in Brazil’s major soybean-producing regions. In addition to acreage expansion, yield of 51.6 bushels per acre were the highest ever for the country. Brazil’s bumper soybean crop last year had a huge impact on global markets, as China sought alternative supplies amid a trade war with the US.
NDVI satellite data, a core part of Gro’s data platform, is a powerful indicator of plant health, detecting positive signals and plant stressors as much as two weeks before such issues are apparent to the naked eye. Simple maps of NDVI readings aren’t very helpful, partly because they fail to distinguish between crops and extraneous vegetation. With proper masking, however, NDVI becomes a vital component of reliable crop yield models, along with other variables such as soil moisture, temperature, and precipitation. Industry players across the agricultural sector, including traders and food, beverage, and chemical companies, can benefit from building predictive models which incorporate NDVI to better inform their decision-making.
Receive our research in your inbox
Thank you for subscribing to our newsletter!
What Information Do We Collect?
The information we gather enables us to personalize, improve and continue to operate the Services. We collect the following types of information from our users.
IP Address Information and Other Information Collected Automatically:
· We automatically receive and record information from your web browser when you interact with the Services, including your IP address and cookie information. This information is used for fighting spam/malware and also to facilitate collection of data concerning your interaction with the Services (e.g., what links you have clicked on).
· Generally, the Services automatically collect usage information, such as the number and frequency of visitors to the Site. We may use this data in aggregate form, that is, as a statistical measure, but not in a manner that would identify you personally. This type of aggregate data enables us and third parties authorized by us to figure out how often individuals use parts of the Services so that we can analyze and improve them.
Information Collected Using Cookies:
· Most browsers have an option for turning off the cookie feature, which will prevent your browser from accepting new cookies, as well as (depending on the sophistication of your browser software) allowing you to decide on acceptance of each new cookie in a variety of ways.
We collect statistical information about how users collectively use the Services (“Aggregate Information”). Some of this information may be derived from Personal Information. This statistical information is not Personal Information and cannot be tied back to you or your web browser.
How, and With Whom, Is My Information Shared?
IP Address Information:
Information You Elect to Share:
We share Aggregate Information with our partners, service providers and other persons with whom we conduct business. We share this type of statistical data so that our partners can understand how and how often people use our Services and their services or websites, which facilitates improving both their services and how our Services interface with them. In addition, these third parties may share with us non-private, aggregated or otherwise non Personal Information about you that they have independently developed or acquired.
Information Shared with Our Agents:
We employ and contract with people and other entities that perform certain tasks on our behalf and who are under our control (our “Agents”). We may need to share Personal Information with our Agents in order to provide products or services to you. Unless we tell you differently, our Agents do not have any right to use Personal Information or other information we share with them beyond what is necessary to assist us. You hereby consent to our sharing of Personal Information with our Agents.
Information Disclosed Pursuant to Business Transfers:
In some cases, we may choose to buy or sell assets. In these types of transactions, user information is typically one of the transferred business assets. Moreover, if we, or substantially all of our assets, were acquired, or if we go out of business or enter bankruptcy, user information would be one of the assets that is transferred or acquired by a third party. You acknowledge that such transfers may occur, and that any acquirer of us or our assets may continue to use your Personal Information as set forth in this policy.
Information Disclosed for Our Protection and the Protection of Others:
Information We Share With Your Consent:
Except as set forth above, you will be notified when your Personal Information may be shared with third parties, and will be able to prevent the sharing of this information.
Is Information About Me Secure?
We store all of our information, including your IP address information, using industry-standard techniques. We do not guarantee or warrant that such techniques will prevent unauthorized access to information about you that we store, Personal Information or otherwise.
What Information of Mine Can I Access?
You can access and delete cookies through your web browser settings.
California Privacy Rights: Under California Civil Code sections 1798.83-1798.84, California residents are entitled to ask us for a notice identifying the categories of personal customer information which we share with our affiliates and/or third parties for marketing purposes, and providing contact information for such affiliates and/or third parties. If you are a California resident and would like a copy of this notice, please submit a written request to the following address: 12 E 49th Street, 11th Floor, New York, NY 10017
What If I Have Questions or Concerns?
If you have any questions or concerns regarding privacy using the Services, please send us a detailed message to firstname.lastname@example.org. We will make every effort to resolve your concerns.
Effective Date: March 11, 2014
b. You shall not (directly or indirectly):i. take any action that imposes or may impose (as determined by us in our sole discretion) an unreasonable or disproportionately large load on our (or our third party providers’) infrastructure;ii. interfere or attempt to interfere with the proper working of the Services or any activities conducted on the Services;iii. bypass, circumvent or attempt to bypass or circumvent any measures we may use to prevent or restrict access to the Services (or other accounts, computer systems or networks connected to the Services);iv. use manual or automated software, devices, or other processes to “crawl” or “spider” any page of the Site;
v. harvest or scrape any Content from the Services;
vi. otherwise take any action in violation of our guidelines and policies;vii. decipher, decompile, disassemble, reverse engineer or otherwise attempt to derive any source code or underlying ideas or algorithms of any part of the Services (including without limitation any application), except to the limited extent applicable laws specifically prohibit such restriction;viii. modify, translate, or otherwise create derivative works of any part of the Services; orix. copy, rent, lease, distribute, or otherwise transfer any of the rights that you receive hereunder.c. We also reserve the right to access, read, preserve, and disclose any information as we reasonably believe is necessary to:i. satisfy any applicable law, regulation, legal process or governmental request;ii. enforce these Terms of Service, including investigation of potential violations hereof;
iii. detect, prevent, or otherwise address fraud, security or technical issues;
iv. respond to user support requests; or
v. protect the rights, property or safety of us, our users and the public.4. Third Party Services. The Services may permit you to link to other websites, services or resources on the Internet, and other websites, services or resources may contain links to the Services. When you access third party resources on the Internet, you do so at your own risk. These other resources are not under our control, and you acknowledge that we are not responsible or liable for the content, functions, accuracy, legality, appropriateness or any other aspect of such websites or resources. The inclusion of any such link does not imply our endorsement or any association between us and their operators. You further acknowledge and agree that we shall not be responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with the use of or reliance on any such content, goods or services available on or through any such website or resource.5. Termination. We may terminate your access to all or any part of the Services at any time, with or without cause, with or without notice, effective immediately. All provisions of these Terms of Service which by their nature should survive termination shall survive termination, including, without limitation, ownership provisions, warranty disclaimers, indemnity and limitations of liability.6. Warranty Disclaimer.a. You release us from all liability for you having acquired or not acquired Content through the Services. We make no representations concerning any Content contained in or accessed through the Services, and we will not be responsible or liable for the accuracy, copyright compliance, or legality of material or Content contained in or accessed through the Services.b. THE SERVICES AND CONTENT ARE PROVIDED “AS IS”, “AS AVAILABLE” AND WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF TITLE, NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, AND ANY WARRANTIES IMPLIED BY ANY COURSE OF PERFORMANCE OR USAGE OF TRADE, ALL OF WHICH ARE EXPRESSLY DISCLAIMED. WE, AND OUR DIRECTORS, EMPLOYEES, AGENTS, SUPPLIERS, PARTNERS AND CONTENT PROVIDERS DO NOT WARRANT THAT: (I) THE SERVICES WILL BE SECURE OR AVAILABLE AT ANY PARTICULAR TIME OR LOCATION; (II) ANY DEFECTS OR ERRORS WILL BE CORRECTED; (III) ANY CONTENT AVAILABLE AT OR THROUGH THE SERVICES IS FREE OF VIRUSES OR OTHER HARMFUL COMPONENTS; OR (IV) THE RESULTS OF USING THE SERVICES WILL MEET YOUR REQUIREMENTS.7. Limitation of Liability. IN NO EVENT SHALL WE, NOR OUR DIRECTORS, EMPLOYEES, AGENTS, PARTNERS, SUPPLIERS OR CONTENT PROVIDERS, BE LIABLE UNDER CONTRACT, TORT, STRICT LIABILITY, NEGLIGENCE OR ANY OTHER LEGAL OR EQUITABLE THEORY WITH RESPECT TO THE SERVICES FOR ANY (I) LOST PROFITS, DATA LOSS, COST OF PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, OR SPECIAL, INDIRECT, INCIDENTAL, PUNITIVE, COMPENSATORY OR CONSEQUENTIAL DAMAGES OF ANY KIND WHATSOEVER, SUBSTITUTE GOODS OR SERVICES (HOWEVER ARISING), (II) BUGS, VIRUSES, TROJAN HORSES, OR THE LIKE (REGARDLESS OF THE SOURCE OF ORIGINATION), OR (III) DIRECT DAMAGES IN EXCESS OF $50.00.8. Governing Law and Jurisdiction. These Terms of Service shall be governed by and construed in accordance with the laws of the State of New York, including its conflicts of law rules, and the United States of America. You agree that any dispute arising from or relating to the subject matter of these Terms of Service shall be governed by the exclusive jurisdiction and venue of the state and Federal courts of New York County, New York.9. Miscellaneous.a. Modification. We reserve the right, in our sole discretion, to modify or replace any of these Terms of Service, or change, suspend, or discontinue the Services at any time. Your continued use of the Services following notification of any changes to these Terms of Service constitutes acceptance of those changes.b. Entire Agreement and Severability. These Terms of Service are the entire agreement between you and us with respect to the Services, including use of the Site, and supersede all prior or contemporaneous communications and proposals (whether oral, written or electronic) between you and us with respect to the Services. If any provision of these Terms of Service is found to be unenforceable or invalid, that provision will be limited or eliminated to the minimum extent necessary so that these Terms of Service will otherwise remain in full force and effect and enforceable. The failure of either party to exercise in any respect any right provided for herein shall not be deemed a waiver of any further rights hereunderc. Force Majeure. We shall not be liable for any failure to perform our obligations hereunder where such failure results from any cause beyond our reasonable control, including, without limitation, mechanical, electronic or communications failure or degradation.d. Assignment. These Terms of Service are personal to you, and are not assignable, transferable or sublicensable by you except with our prior written consent. We may assign, transfer or delegate any of our rights and obligations hereunder without consent.e. Agency. No agency, partnership, joint venture, or employment relationship is created as a result of these Terms of Service and neither party has any authority of any kind to bind the other in any respect.f. Notices. Unless otherwise specified in these Term of Service, all notices under these Terms of Service will be in writing and will be deemed to have been duly given when received, if personally delivered or sent by certified or registered mail, return receipt requested; when receipt is electronically confirmed, if transmitted by facsimile or e-mail; or the day after it is sent, if sent for next day delivery by recognized overnight delivery service. Electronic notices should be sent to email@example.com. No Waiver. Our failure to enforce any part of these Terms of Service shall not constitute a waiver of our right to later enforce that or any other part of these Terms of Service. Waiver of compliance in any particular instance does not mean that we will waive compliance in the future. In order for any waiver of compliance with these Terms of Service to be binding, we must provide you with written notice of such waiver through one of our authorized representatives.h. Headings. The section and paragraph headings in these Terms of Service are for convenience only and shall not affect their interpretation.Contact. You may contact us at the following address: 12 E 49th Street, 11th Floor, New York, NY 10017.