According to the United Nations High Commissioner for Refugees (UNHCR), the UN’s refugee agency, 123,300 refugees crossed the Mediterranean in 2021. The global Covid-19 pandemic reduced these numbers in 2020 to 95,800, but 123,700 made the dangerous trip across the sea in 2019. UNHCR says that 3,231 of these refugees were reported as dead or missing as they crossed from Africa and the Middle East towards Europe. This figure does not account for those who die or go missing during land crossings through remote areas like the Sahara Desert towards the coast of North Africa to head for a better life in Europe.
The European Union’s Frontex border control agency estimates that some 20,000 have died or gone missing since 2015. For the authorities patrolling the Mediterranean, locating tiny boats full of refugees is a vexing challenge. The Mediterranean Sea covers an area of 728,883 square nautical miles/nm (2.5 million square kilometers/km). Trying to find a boat in such an expanse is like trying to find a particular stone on a pebble beach.
Traditionally, coastguard and border patrol vessels and aircraft covering the Mediterranean have used sophisticated electro-optical systems to find the small vessels. Infrared and night vision helps locate the boats in darkness and low visibility. Radar may assist provided it is suitably calibrated to find small boats in what may be rough and undulating waters. Humans’ ‘Mk.1 eyeballs’ meanwhile can be enhanced with binoculars. Nonetheless, these is no perfect way to find all the boats all the time. Finding these small craft is important, not only for law enforcement but most importantly to prevent loss of life. As the above paragraph notes, figures show that crossing the Mediterranean can be dangerous. Like any sea, storms present dangers and fine weather can turn foul in a heartbeat. The layperson maybe unaware that the Mediterranean can suffer medicanes. Although these sounds like over-the-counter painkillers, a medicane is the Mediterranean equivalent of a hurricane. While not necessarily as violent as their tropical Hurricane cousins, they can still unleash deadly force. Violent storms can increase during the last five months of the year.
UNHCR says that 3,231 refugees were reported as dead or missing as they crossed from Africa and the Middle East towards Europe
Added to the weather hazards is the fact that boats maybe overloaded and likely to founder. Those onboard may have rudimentary navigation systems. These may extend to little more than standard Global Navigation Satellite System (GNSS) equipment. Some occupants maybe unable to swim and the boats may lack life-saving equipment. Finally, the boats themselves maybe completely unsuitable for the voyage they are to perform.
However, some or all of the occupants may have cellphones. They may even have been given a satellite phone by the traffickers organizing the refugees’ trip. Both cellphones and satphones transmit radio waves. These transmissions can be exploited by rescuers to find boats which may be in trouble.
Traffickers use three main routes to smuggle refugees into Europe via the Mediterranean. The Western Route is across the Strait of Gibraltar from Morocco. The Central Route stretches from Libya and Tunisia towards Sicily. The Eastern Route goes from Turkey to Greece. According to Frontex’ figures 637,2,150 and 1,162 refugees may have used these routes during the first month of 2022.
Frontex has three separate operations spanning these routes: Operation Indalo covers the Western Route, Operation Themis the Central Route, and Operation Poseidon the Eastern Route. Efforts to combat people smuggling from the Libyan coast have included operations Sophia and Irini. The latter ran from 2015 until 2020 before being replaced by the former, aimed primarily at upholding the UN arms embargo on Libya. These latter operations are run by the European Union’s EUNAVFOR naval force. Alongside navies, border guards, coastguards and police help locate refugees either when at sea or once they make landfall.
Finding the signal
As noted above, cellphones and satphones transmit and receive radio waves. In theory any device which transmits a radio wave can be detected by a radio receiver in range of the transmitter. Radio waves travel in a straight line at the speed of light (161,595 knots-per-second/299,274 kilometers-per-second). For a radio receiver to detect transmission, it must have a clear line-of-sight between the two. Mountains, buildings, rough oceans, and Earth’s horizon can obscure this line-of-sight. This may cause radio waves to become distorted or not be received at all.
There is every chance that refugee boats will suffer difficulties, or worse, on their dangerous Mediterranean crossing. For the occupants getting rescued will be paramount, but how do you find a small boat across thousands of square nautical miles of sea? The first thing that many of the occupants will do upon perceiving danger is make a call. If they have cellphones, they may try to call relatives back home to raise the alarm. Alternatively, they may have found or been given numbers of local coastguard agencies, charities, or law enforcement organizations prior to their voyage. The chances of their cellphone call being successful if the boat is at sea and out of coastal cellphone coverage are minimal.
Nonetheless, the phone is now transmitting a signal and trying to connect with a network. This outgoing transmission can be detected and located. Sources involved in refugee rescue have shared with the author that people traffickers will sometimes provide each boat with a single satphone. This will be preloaded with numbers of rescue organizations that can be called in an emergency. Like the cellphone, the satphone makes a radio transmission to connect with a satellite overhead. Unlike the cellphone, these transmissions will be able to reach a rescue organization as they can bounce off the satellite to their intended destination.
Radio receivers can cover specific wavebands used by cellphones and satphones. Both tend to use allotted frequencies in the very and ultra-high frequency wavebands of 30 megahertz/MHz to three gigahertz. Receivers not only detect when a cellphone or satphone is transmitting. They can also accurately determine the source of those transmissions. This is done using the Time Difference (TDOA) approach. As all radio waves travel at the speed of light this means they will reach different points at different times. Suppose we have a radio receiver with two receiving antennas tuned to a cellphone’s frequency two meters (six feet) apart. The cellphone’s signal will reach the antenna nearest the phone slightly earlier than the transmitter further away. The speed of the radio waves means that the difference in time of arrival will be microscopically small, but they exist nonetheless. TDOA lets the radio receiver then draw a bearing from each of the antennas based on the time difference. The point where the two bearings meet is the location of the source of transmission. The source of the transmission is where the phone is located. This process lets rescuers accurately determine the location of the boat in distress. The speed of radio transmissions means this is a process that can be performed rapidly as the receivers’ sophisticated software performs the required calculations in an instant.
The higher the radio receiver’s antenna is positioned the longer its range to detect the transmissions of those in distress. Much like our own eyes, the higher the antennas are, the further they see. A receiving antenna placed on top a coastguard vessel’s mast will have a detection range of circa 9.7nm (18km). Beyond this, the curvature of the Earth will obscure the phone transmissions. Place the radio receiver on an aircraft and this increases significantly. A receiver adorning a plane flying at 20,000 feet/ft (6,096 metres) has a detection range of 173nm (321km).
Little surprise that these receivers are now being used in the Mediterranean to help find refugees in distress. They are equipping aircraft supporting Frontex’ efforts. Horizon Technologies produces several systems that can equip aircraft in its FlyingFish product family. One of the notable attributes of FlyingFish is it can detect and locate satphone transmissions using the Thuraya satellite constellation. Thuraya phones use frequencies of 1.525GHz to 1.661GHz. Usefully, these phones automatically periodically transmit their coordinates derived from the GNSS signals they receive. For example, the phone may receive signals from the US Global Positioning System constellation. It then automatically sends its coordinates out into the ether.
FlyingFish detects not only the Thuraya phone transmissions but also these GNSS signals. Thus, someone in a maritime surveillance aircraft equipped with this payload gets the immediate coordinates of the phone. FlyingFish also detects and locates transmissions from satphones using the INMARSAT constellation. FlyingFish has been augmented by Horizon’s BlackFish product. This also detects and locates satphones using the Iridium network alongside Thuraya and INMARSAT.
A single CubeSat at 2,000 kilometers’ altitude can cover 3,657,571 square nautical miles
Systems like FlyingFish and BlackFish are most useful when equipping aircraft to provide long detection ranges. Frontex makes extensive use of aircraft to support its Mediterranean mission. A range of platforms including Diamond DA-42/62 and Beechcraft Super King Air-350 twin turboprop aircraft. These have supported the Frontex mission alongside Israel Aerospace Industries Heron-1 uninhabited aerial vehicles.
Over the longer term, radio monitoring over the Mediterranean will improve with the advent of space-based capabilities. The world is witnessing a minor revolution in the space sector with the advent of technologies like CubeSats is ‘democratizing’ access to the cosmos. CubeSats typically have a mass under two kilograms (4.4 pounds/lbs). Mass is critical where satellites are concerned. Launching spacecraft is not cheap, but prices are coming down. A satellite launch by the National Aeronautics and Space Administration’s Space Shuttle would cost $60,000 per kilogram. It costs $1,200 per kilogram (2.2lbs) to launch a satellite using SpaceX’s Falcon-9 rocket. This makes it economical to place scores of CubeSats can be placed in low earth orbits of below 1,079nm (2,000km) above Earth.
Cubesats could be positioned in low earth orbits above the Mediterranean equipped with radio receivers to listen for tell-tale signals from cellphones or satphones. This could be done for comparatively less money than a single conventional satellite performing the same mission. The relatively low costs for CubeSats means they are relatively inexpensive to replace once they reach the end of their lives.
CubeSats have another major benefit as they do not suffer from human fatigue and can maintain a longer time on station. An aircraft with a radio receiver can perform its mission for as long as its fuel reserves and human reserves allow. Despite being detecting signals almost two hundred nautical miles from the aircraft, depending on altitude, an airborne radio receiver is limited in the area it covers. An aircraft flying at 20,000ft covers an area of 94,024 square nautical miles (322,493 square kilometers), twelve percent of the Mediterranean. A single CubeSat at 2,000 kilometers’ altitude can cover 3,657,571 square nautical miles (12,545,117 square kilometers). This is over five times the area of the Mediterranean. CubeSats could play a useful role in helping to detect the cellphone and satphone signals of those in distress when aircraft with radio receivers are not flying.
We are arguably at the dawn of radio receiving technologies’ potential as a rescue tool. Airborne radio monitoring systems are making their presence felt. The transposition of this technology into space could yet pay more dividends. The movement of people across the Mediterranean shows no signs of abating. Detecting those in distress through their communications signals will help get them to safety.