Global population is predicted to increase to almost ten billion people by 2050, requiring food production to increase by 70%. At the same time, the amount of land available to grow crops is declining rapidly, with 95% of the world's fare grown in soil. It is, therefore, incumbent that fields are used as efficiently as possible to guarantee security of food supply and long-term sustainability.

Farmers assessing their fields only get a limited view when visually checking for damage, weeds, or pests. Remote sensing using Earth observation satellites provide growers an aerial view to make quicker and more accurate assessments of their crops. Hyperspectral optical and synthetic aperture radar imagers measure the sunlight reflected by plants (greenness), fluorescence (productivity/growth rate of each plant), and soil quality to optimise yields.

These observations are complemented by IoT sensors on the ground which determine soil moisture, pH, and leaf wetness, providing farmers near-realtime status of the cultivation of their fields. If data suggests they need to spray their plants with water, fertiliser, or pesticides, growers can combine the results with GPS data to instruct tractors how much treatment to apply, at which rate, and where in the field enabling true-precision farming.

ESA's Fluorescence Explorer
Figure 1
Illustration of ESA's Fluorescence Explorer mission to quantify photosynthesis
Source: ESA

Earth observation satellites are increasingly using passive hyperspectral sensors to measure the reflected sunlight in the visible and infrared wavelengths from objects within its field of view (swath). Hundreds of bands of information for every pixel are collected and signatures are generated that are uniquely characteristic of plant physiology, crop health, and plant speciation.

As the satellite orbits Earth, hyperspectral sensors capture individual slices of the incoming view through a physical slit and breaks this into discrete wavelength components onto a focal plane array. The system then separates the light in each spatial pixel into the different colours as shown below. Each time the camera takes a picture through the slit, it gets a full frame of spectral data for each pixel. Stacking up each image, as the spacecraft moves over the scene, builds a cube of hyperspectral data. High-throughput payloads exploiting ultra-deep submicron FPGAs are being used to process this information. The ability to distinguish certain wavelengths is called spectral resolution and different materials have unique signatures. Spatial resolution is the measure of the observable detail in an image, from sub-meter to tens of kms, and is a function of the area/footprint viewed by the satellite known as the swath.

Figure 2
Hyperspectral image capture and generation of resulting spectral data

To allow realtime, high-resolution monitoring when there is cloud cover, inclement weather, or during the night, an active sensor is used, such as a synthetic aperture radar (SAR). Radio waves are transmitted to 'illuminate' the target scene and the echo of each pulse is received, digitized, and processed to reconstruct 2D, 3D, and 4D (space and time) imaged views. The amplitude and phase of the backscattered signal depends on the physical (geometry and roughness) and electrical (permittivity) properties of the reflected scene. In the case of spaceborne SAR, as a satellite moves, transmission and reception occur at different positions within its orbit allowing the construction of a virtual aperture that is much longer than the physical antenna length.

Figure 3
SAR-based Earth observation in cloudy conditions

Global warming compounds guaranteeing security of food supply and long-term sustainability: most human activity has some impact on the environment or on specific ecosystems and this situation will only get worse as population increases. The need for continued economic development relies on activities which traditionally damage the environment and NASA's Global Climate Change website displays key vital signs some of which are alarming to say the least. Satellites provide a global view of land and sea temperatures and ESA has created the Climate Change Initiative which integrates datasets from different missions to produce comprehensive, long-term records.

A combination of depleting groundwater resources, climate change, and extreme natural disasters are resulting in poor yields and crop loss in certain parts of India. Each year, the delays caused by institutional apathy are causing 12,000 farmers living below the poverty line to take their own lives. To address this tragic situation, satellite data complemented by information from IoT sensors, is now being used to provide insurers accurate estimates of plant growth in realtime allowing farmers to receive compensation speedily.

To guarantee security of food supply and long-term sustainability, the situation at sea is equally dim: it is estimated that up to 20% of all fish caught is done so illegally, depleting the world's oceans of their precious marine stocks. Today, over one billion people in developing countries rely on fish as their primary source of protein.

Managing sustainability at sea-level is almost impossible due to the sheer number of vessels spread across the Earth's seas and oceans. Furthermore, boats engaging in unregulated and unreported fishing can simply turn-off their navigational, positional tracking, and avoidance system (AIS). Satellites allow realtime monitoring of vessels, fishing methods and suspicious behaviour using optical, infrared, and SAR sensors in all weather conditions and also at night.

If you would like to learn more about Earth observation measurements using satellite technology, ESA offers a free, five-week online course. The following video provides further details about this training:

Until next month, the first person to tell me the difference between SAR and conventional radar will win a Courses for Rocket Scientists World Tour t-shirt. Congratulations to Gunter from Austria, the first to answer the riddle from my previous post: BRAVE new ITAR/EAR-free space-grade FPGAs.

Rajan Bedi is the CEO and founder of Spacechips, which provides on-board processing products, design consultancy in space electronics, training, technical-marketing, and business-intelligence services.

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