Using spatial and aerial imagery to estimate crop surfaces in developing countries

Agricultural statistics are essential for monitoring production changes, planning government interventions and future investments, and estimating crop outputs for policymakers, researchers, and organizations. Poor agricultural data can lead to disastrous misallocations of resources and unsuccessful policies, as well as having a dire impact on populations and farmers alike.

 
Rwanda fields
 

 

Jacques Delincé, a veteran agricultural statistician and former head of Agrilife and MARS units at the European Commission, is currently working as a consultant for the Food and Agriculture Organization – or FAO – on the Global Strategy to improve Agriculture and Rural Statistics. The team is looking for more cost-efficient methods for agricultural statistics in developing countries and, in particular, comparing the accuracy and costs of list and area frames for farmer surveys.

Estimating crop areas by conducting farmer interviews involves collecting data through regular household questionnaires, asking farmers to estimate the superficies of planted crops for an individual field or farm. Area frame surveys, on the other hand, is a global estimate drawn from a sample collection of well-defined land units.

In Nepal and Brazil, the FAO ran ground data collection surveys. Ground surveys have many strengths, but can also be costly and strict quality control procedures are needed to ensure data integrity. And, despite rigorous statistical modeling approaches, accuracy remains an issue as cost considerations often restrict sample sizes.

This could drastically change in the next few years as Earth observation data becomes more accessible and affordable satellite imagery can be used to supplement ground based systems. And in areas where surveys are unsafe due to civil wars and violence, aerial images may be the only approach.

In the interest of saving costs while working in Rwanda, Delincé and his team opted to use ground surveys from the current year and combine them with recent remote-sensed data. If the team could obtain crop area results similar enough to the ground surveys by analyzing aerial images from the same location, then Delincé could apply the same discriminating methodology to satellite images of the entire country to get an accurate estimate of crop surface areas.

For their analysis, Global Strategy’s team started with images from Sentinel-2, Landsat-8, and Sentinel-1. Rwanda is around 25,000 km2, roughly the size of Maryland. With a country of this size, it is often more economical to use satellite imagery over drones or planes.

Drones can be a great tool to cover small, defined areas, but regulations can vary greatly by location. For example, rules such as line-of-sight, requiring the pilot to be able to see the drone at all times, or large no-fly zones around buildings, like airports or hospital with helipads, represent a serious hurdle to full area coverage.

Planes, on the other hand, efficiently cover very large surfaces, are less susceptible to cloud coverage issues often plaguing satellites, and offer significant savings over very high-resolution satellite images. But, as with drones, military or government restrictions prevent statisticians and scientists to fly over certain areas.

Accurately estimating crop areas from aerial images is never easy and is even more of a challenge in the context of African farming systems. Crop areas in Sub-Saharan Africa are often characterized by smallholder farms that produce a wide range of diverse crops, non-uniform plots in a wide range of sizes – sometimes of the order of a few meters square – and intercropping, where farmers plant different crops within the same field.

Rwanda is no exception and the preliminary results from the study were inconclusive. The spatial resolution of open data used was too coarse, at 15 and 10 m, to properly distinguish between cultures. Despite this, through Global Strategy’s research, the Rwandan governments and NGOs, both global and local, will be able to better estimate future crop allocation, develop help plans for farmers, and even model the impact of specific food subsidies on the local economy.

To improve results accuracy further and widen the applicability, the team is now looking into sub-meter satellite data. As satellite sensors continue to sharpen and Earth observation data access improves over time, programs like the FAO Global Strategy will develop even more cost-efficient methods to improve Agriculture and Rural Statistic for developing countries.


 

You might also be interested in

 
 
 

What resolution do I need when using satellite Earth observation data?

Trick question: it depends on what you are trying to do.

What does resolution mean?

When it comes to Earth observation, you might hear about spatial resolution, spectral resolution, and temporal resolution. While all three need to be considered when looking for the satellite data, most often, when people ask about resolution, they mean “spatial resolution”.

Spatial resolution is the size of one pixel on the ground. Pixel stands for 'picture element' – the smallest individual 'block' that makes up the image. With a finer spatial resolution, 30 cm for example  – where each pixel represents a 30 x 30 cm area, for optical data – you would be able to distinguish details, such as houses or cars. With a coarser resolution, an image of a similar digital size would cover a much larger surface on Earth and smaller features become harder to distinguish.

Note from the SkyWatch SAR expert: The above definition only applies to optical data. Synthetic aperture radar data (SAR) is not acquired at nadir like optical data but rather on a slant. Therefore the data is in slant range and the pixels on the ground are not square.

To better illustrate, here are two satellite pictures of the same location (Burj Khalifa, Dubai) taken with different spatial resolution sensors. On the left, a 30 cm resolution from Triple Sat Constellation, on the right, a 15 m resolution from Landsat-8

Dubai comparison high resolution satellite data vs coarse resolution

Spectral resolution is related to the granularity of the breadth of coverage of the electromagnetic spectrum captured by the satellite sensors. A finer spectral resolution can discriminate between narrower bands of wavelength, differentiating, for example, between red, green, and blue bands and allowing for coloured images.

Wavelength spectrum

Satellite sensors are able to capture data that would be invisible to the naked eye and a higher spectral resolution can provide us with a different view of objects and landscapes. For example, the shortwave infrared ranges enable highly effective geological mapping, because rocks and minerals have their own spectral pattern in these bands.

Temporal resolution refers to the time elapsed between viewings of the same area on Earth at the same angle. It can range from continuous coverage for geostationary platforms – such as a weather satellite, set at a fixed point over the Earth’s surface – to several days between revisits for low earth orbiting platforms (LEO). A higher temporal resolution means a shorter revisit time.

What resolutions are available in 2017?

Spatial resolution for Earth observation satellites in the early 1980s  was around 80 m – as was available on Landsat-4. Now, you can find remote-sensing data to purchase with spatial resolutions as low as 30 cm. For open data, some of the finer sensor can capture up to 15 m resolution images.

The spectral resolution also improved drastically over the past few decades, as sensors were refined and more bands became available for study. Some of the most recent satellites sensors can now capture information on more than 1,000 different spectral bands.

As for temporal resolution, it is still very much varies based on the satellite. However, if you are interested in data regarding one specific area, the sheer amount of satellites that were launched has increased your chances of obtaining multiple, non cloud-covered, usable pictures.

Why a higher spatial resolution is not always better?

Higher costs

Higher spatial and spectral resolutions can be obtained by using the most recent technology. This usually requires heavy investments and this data can be extremely pricey. Additionally, thanks to the Copernicus program and the Landsat program, large amount of coarser resolution satellite data archives are available for viewing and download. Open satellite data can be obtained for free through the SkyWatch API.

Less consistency

Newer commercial satellites often work on a “tasking” basis, which means clients could request a specific satellite to cover a certain area at a certain time. If a priority account task the satellite you relied on, the data you needed might get delayed or simply not be available. When it comes to larger government programs, like Landsat and Sentinel, images are systematically acquired instead of tasked – these satellites follow consistent paths and rhythms – which means you can expect to always get an image in the same mode without worrying about conflicts.

Smaller areas

Covering the same surface area with a 50 cm spatial resolution would render an image with 20 times the amount of pixels than the same surface covered by a 10 m sensor. This means an image of the same area will be a much larger file, and of course, take longer to download. This can be an important consideration factor when building an app.

Lower availability

While some of the most recent satellites can offer imagery up to 25 cm resolution, a large number of  satellites currently circling the Earth have sensors that only offer coarser resolutions – in today’s standards. Additionally, data collected by older satellites from the Landsat and Copernicus programs over the past decades have been made freely available. As a result, specifying a coarser spatial resolution is likely to drastically enhance your chances of obtaining more than one image for the same area.

Shorter time period

With the improvements in sensor technology, for the first time in the early 2000, IKONOS made sub-meter resolution images available for purchase. Numerous satellites offering commercially available very high resolution images have since then been successfully launched. However, in studies of longer trends will require to use data that could be 10, 20, or 30 years old and will have a coarser resolution.

Scale

Numerous satellite data applications, such as climate studies, look at larger patterns and global trends. In such cases, short revisit rates, and high spectral resolution are key to answering questions and global data from Sentinel-3 and MODIS are more valuable than sub-meter imagery. A coarser spatial resolution would actually be preferred.

How to decide which spatial resolution you need?

Our advice, when doing remote-sensing data analysis or building a space app: think first about what you are trying to achieve and what resolutions you need to solve your business problem.The most detailed spatial resolution may not always be the best.

For example, a consortium, led by the Joint Research Centre (JRC) has successfully combined data from multiple coarser resolution satellites to monitor forest fires, using each satellite to compensate for the deficiencies from the other sensor – cloud perturbations for Sentinel-2 and sensitivity to ground moisture for Sentinel-1.

Continuous improvements in sensors, as well as the higher amount of available satellite data have helped dramatically expand the applications of satellite imagery and the possibilities are now almost limitless.


 

You might also be interested in

 
 
 

Monitoring forest fires

Between November 2015 and April 2016, over 36,000 hectare of forest was burnt in the Republic of Congo. The main commercial activity in the area is the extraction of round wood from areas leased from the national authorities by private companies. These cover an extensive part of forest in the north of the country including the Marantaceae forests, which were affected by the fires. 

While it is usually too humid for forests to burn in the area, a very strong El Niño caused a high number of fires to spread at the beginning of 2016. During peak times,  the fires were spreading as fast as 1,600 hectares a day, making it especially dangerous to track through conventional ways.

The Congolese forests are not only the primary habitat for many large mammals, such as gorillas and forest elephants, but they are also an important carbon storage for the world. 

In order to determine the source of the fires and help monitor the spread to better allocate resources to combat and prevention, a consortium, led by the Joint Research Centre used satellite data from both Sentinel-1 and Sentinel-2 — each satellite's sensor compensating for the difficulty of the other (cloud perturbations for Sentinel-2 and sensitivity to ground moisture for Sentinel-1).

"Burnt areas mapped by Sentinel-1's synthetic aperture radar and Sentinel-2's multispectral imagery highlighted that the origin of the fires correlates with accessibility to the forest, suggesting they were caused by human activity.

With a temporal resolution of 10 days and a spatial resolution of 10 m, Sentinel-2A images allow the timing and extent of fire events to be mapped precisely. This is an improvement on the temporal resolution of 16 days and spatial resolution of 30 m that Landsat-8 provides."

Source: Verhegghen et al, 2016

 


 

You might also be interested in

 
 
 

5 Ways Satellite Data Can be Used to Improve Global Health

The phrases “satellite data” and “improving worldwide healthcare” aren’t typically used in the same sentence. In fact, a vast majority of satellite data conversations are focused on a few narrow applications in the natural resource industries (i.e. mining, oil & gas, forestry, agriculture, energy, etc.). But satellite data, and more specifically earth-observation imagery, can be used for many causes outside this small scope. The healthcare industry is a great example. By looking for a variety of different clues within satellite imagery, we can learn a great deal about the health and health-risk of a population. Armed with this information, healthcare organizations can be more proactive and responsive in treating patients around the globe. The following are 5 ways satellite data can be used to improve global health.

5. Monitoring Water Levels and Water Evaporation

According to the United Nations, as of 2013, over 2.5 billion people do not have access to safe drinking water. And this number is only increasing. Water management will become one of humanity’s most crucial tasks in the not-too-distant future. As populations continue to grow and climate change impacts our hydrosphere, access to clean water - even for nations which currently enjoy this luxury - may not come easily. Monitoring the water levels in rivers and lakes, the volume of evaporation, ground moisture content, and the proportion of pollutants in the air which can affect water quality (i.e. acid rain), is no longer just interesting. It is necessary for the survival of millions. This is where climate satellites can help. After they have been placed in orbit, satellites are a low-cost method of observing the Earth’s water cycle. The information they provide can be used to help ensure the health of as many populations by optimizing safe and clean water access around the planet.

4. Identifying Dangerous Mosquito Populations

Mosquitoes are known carriers of a wide range of deadly diseases like malaria, yellow fever, tuberculosis, and more. While these tiny killers themselves cannot be detected by commercial satellites, we can identify the environmental characteristics of their habitats. Appropriate breeding ground for mosquitoes vary by species and can be identified based on the combination of plant type, ground cover, air quality, and volume of water present in a specific area. Remote sensing specialists use both multispectral and hyperspectral satellites to identify the location of mosquito breeding, the inhabiting species, and the risk that these insects have come in contact this a deadly disease. This data allows healthcare professionals to more accurately estimate the extent of treatment required and the strategy behind a response. This technology directly impacts those in areas where healthcare is lacking and mosquito-borne diseases are prominent.

3. Measuring Air-Borne Particulate Levels

“Filtering particulates from air makes a significant [and] measurable diff[erence] to health.” This is a quote from Elon Musk, which he tweeted in May after announcing his electric vehicle company would be working to integrate an air filtration system into their latest model. While this is not a new or revolutionary idea, it highlights the fact that the business community is starting to invest in a cleaner world though their products. Removing solid pollutants from the world’s air must be a priority, and we can use satellite data to understand which citizens of our planet are at the greatest risk for particulate-related harm. Prior to 2010, it was nearly impossible to create a particulate distribution map, as individual satellites cannot distinguish particulate levels at different altitudes (and in this case, we only care about air quality levels near the Earth’s surface). But then, two scientists in Canada combined the datasets of multiple NASA satellites to create a vertical profile of the Earth air-borne particulate levels. With this information, health care experts can assess the impact of pollutant-heavy air on public health and, therefore, create targeted solutions for this health risk.

2. Projecting the Severity of Seasonal Allergy Symptoms

Chances are either you or someone you know is affected by seasonal allergies. In America alone, over 40 million adults are subject to itchy eyes and a runny nose come springtime. And unfortunately, these symptoms will only become more severe as levels of atmospheric CO2 continue to increase. The plants which cause these allergies - ragweed, ryegrass, mulberry bushes, etc. - grow very quickly and very large in carbon dioxide rich environments. Even compared to friendlier vegetation like corn, rice, and apple trees, these weeds grow faster in higher levels of when CO2. With more growth, comes more pollen and more severe symptoms for those who are allergic. This means that itchy eyes and a runny nose becomes chest tightness and breathing difficulties. Over-the-counter medication becomes visits to the emergency room. Healthcare professionals must be ready for an increase in patients; satellites can help doctors and nurses prepare for this fluctuation. Satellites like NASA’s Orbiting Carbon Observatory (OCO-2) can be used to detect areas with higher-than-usual levels of CO2. This information can help in predicting which regions of our globe will receive a higher number of allergy patients in their emergency rooms.    

1.   Identifying Large Carbon Emitters

Climate change. Two words that are terrifying to our planet’s next generation of inhabitants. While climate change doesn’t affect humans in the same straightforward way as ingesting air-borne particulates, a hotter Earth can indirectly impact the health of our population. Higher greenhouse gas levels in our atmosphere leads to an increase in tropical storms, wildfires, tornadoes, flooding of coastal cities, and other natural disasters. This means more people are displaced from their homes and “displaced populations have notoriously poor health statistics,” says Aaron Bernstein, Associate Director of the Harvard Medical School’s Center for Health and the Global Environment. Satellites, like NASA’s MOPITT and TES, are monitoring the global levels of greenhouse gasses in the troposphere. While current technology cannot yet identify individual carbon emitters, regional levels can be measured. International pressure can then be placed on the world’s greatest polluters to increase carbon regulation. And once technology has improved, crackdown on large, industrial carbon emitters will vastly decrease the volume of greenhouse gas we are pumping into our planet’s atmosphere. This, in turn, will allow more people the remain happy, and healthy, in their homes.

There are hundreds of satellites currently observing our Earth and hundreds more which will be launched into orbit in the coming years. These instruments allow us to develop a greater understanding of our planet and the effects of our actions on the world’s health. Let’s use this advantage to help improve healthcare around the globe.

If you know of any other ways satellite data can be used to improve healthcare, let us know down below. And if you liked this post, don’t forget to share!

A SpaceX Update: rocket landings, a mouse in space, a parking spot for space taxis, and explosions.

What are SpaceX’s missions for?

SpaceX launch pad at Kennedy Space Center. Photo courtesy of NASA

SpaceX launch pad at Kennedy Space Center. Photo courtesy of NASA

SpaceX’s most recent mission, CRS-9, which was set in motion this week, was the ninth of twenty SpaceX resupply missions commissioned by NASA for $1.6 billion. The goal of CRS-9 was to deliver a Dragon cargo carrier to the International Space Station (ISS) and return the Falcon 9 rocket safely back to land.

Wait, hasn’t a Falcon 9 exploded before?

Falcon 9 from CRS-6 is destroyed on landing. Photo courtesy of @elonmusk.

Falcon 9 from CRS-6 is destroyed on landing. Photo courtesy of @elonmusk.

Yeah, twice. Last year, a loose helium tank caused an unmanned Falcon 9 rocket toexplode two minutes after the CRS-7 mission launch. Another unmanned rocket from the CRS-6 mission exploded in June because of an unstable landing caused by a stuck valve and a resulting mechanical issue. However, this was only a secondary mission. The CRS-6 mission was successful in delivering its Dragon cargo carrier, but the attempted first stage landing resulted in the Falcon 9’s destruction.

Did this rocket survive?

CRS-9 launches. Photo courtesy of Florida’s Space Coast.

CRS-9 launches. Photo courtesy of Florida’s Space Coast.

The Falcon 9 rocket used for CRS-9 successfully detached from its second stage, thenlanded solidly at Cape Canaveral. This created a sonic boom experienced by spectators and people in surrounding areas. A flood of calls to 9–1–1 were placed by people reporting that they were woken up by an explosion.

The CRS-9 first stage landing was SpaceX’s second successful land-landing. Additionally, three first stages have landed successfully on the Autonomous Spaceport Drone Ship (ASDS). As was demonstrated by CRS-9 this week, SpaceX is improving on their goal to bring their rockets safely back to Earth after depositing cargo, as one of SpaceX’s main objectives is to reuse its rockets. Previously, after rockets detached from their second stages, they jettisoned into the ocean and were either rendered useless or they required extensive and expensive repairs in order to be used in another mission. By soft-landing its rockets, SpaceX is saving time and money, and looking pretty cool, too. After several successful Falcon 9 landings, it seems that reusable rockets will become standard as spaceflight becomes more frequent and expands to the private sector.

Did the Dragon make it to the ISS?

The robotic arm grapples the Dragon. Photo courtesy of NASA.

The robotic arm grapples the Dragon. Photo courtesy of NASA.

Yes! After a successful rocket launch, separation of the first and second stages, and return of the first stage to Cape Canaveral, Dragon reached its orbit in ten minutes. The spacecraft chased down the ISS for two days, then was grabbed by a robotic arm and positioned at a docking port. Dragon will return to Earth on August 29.

What is the Dragon carrying?

Heart cells. Photo courtesy of Haixa Wang/Gladstone Institutes

Heart cells. Photo courtesy of Haixa Wang/Gladstone Institutes

The Dragon cargo carrier has on board over 5,000 pounds of equipment and science experiments. This includes a new docking port, the first of which exploded in the failed CRS-7 mission. The docking port will act as a parking spot for “commercial space taxis”. NASA is looking to private space companies to fill the docking port, expecting that a module will lead to the creation of a space station from the private sector once the ISS retires.

The Dragon was also carrying equipment for about 250 scientific experiments never before performed in space. A DNA sequencer will help identify diseases and could later be put to use analyzing extraterrestrial life. For now, it will be performing tests on a virus and a mouse, who, unfortunately, will not ever make the trip back to Earth. In the Dragon delivery was also a sample of live, beating heart cells. These will be tested after a month to check for changes in size, shape, and function. Another test will investigate bone loss in zero-g and compare it to the same test performed in a zero-g simulator stationed on Earth. If the results of the space test and the Earth test are close enough, future experiments will be conducted on Earth. Additionally, Dragon delivered tomato seeds that will later return to Earth to be planted, and microbes that grew out of the radioactive environment at Chernobyl. These microbes will be tested for changes in zero-g and could yield valuable discoveries about radiation treatment.

When Dragon returns on August 29, it will be carrying the results of these experiments, having left the docking port behind for future trips.

Who’s up there to greet the Dragon?

Kate Rubins, Anatoly Ivanishin, and Takuya Onishi before departing on Soyuz spacecraft. Photo courtesy of NASA

Kate Rubins, Anatoly Ivanishin, and Takuya Onishi before departing on Soyuz spacecraft. Photo courtesy of NASA

Two NASA astronauts, including one who worked with the team that developed the DNA sequencer delivered by Dragon, are currently working in the ISS. Additionally, one Japanese astronaut and two Russian cosmonauts are stationed there. A Russian cargo ship, Progress 64, arrived at the ISS two days before Dragon, delivering food and extra supplies for the crew. Progress 64 will stay at the ISS for six months while the crew fills it with trash, then the spacecraft will depart and burn up in the Earth’s atmosphere.

Thanks for reading! If you liked this post, let us know. And don't forget to share! 

[