Telemetry refers to the automatic measurement and wireless transmission of data from remote sensors to centralized data collection and management systems. Such technology is crucial for environmental monitoring, particularly in remote locations where real-time data is essential to meet regulatory requirements or to provide quick notice of environmental conditions.
Telemetry systems can use various communication technologies, each with its own advantages and application scenarios. Some of the most common include cellular, satellite, and various radio protocols. Technically, nearly all forms of over-the-air telemetry common to environmental monitoring are forms of radio communication, but many are commonly known by other names.
What is Cellular Telemetry?
Cellular telemetry transmits data over mobile data (cellular) networks from remote sensors and devices. Its widespread use began in the 1990s with the buildout of GSM/GPRS (2G/2.5G) networks. Modern environmental data collection systems rely primarily on 4G LTE (Long Term Evolution) technology for its high data rates and extensive coverage worldwide.
Cellular telemetry is suitable for applications where real-time data transmission is required, anywhere that reliable 4G coverage is available. Standard LTE offers quick data upload speeds and is generally power-efficient. For low-data rate applications where some latency is acceptable, ultra-efficient LTE standards such as CAT-M (Category M or LTE-M) and NB-IoT (Narrowband IoT) are sometimes used, depending on regional availability1.
5G is also an emerging alternative, particularly in urban smart cities applications where coverage is available. 5G offers significantly higher data rates and greater capacity compared to 4G LTE, which can be useful for applications with continuous measurement and photo or video feeds.
Overall, cellular telemetry is a versatile and widely applicable technology for environmental monitoring, providing reliable and efficient data transmission across various applications and settings.
How Satellite Telemetry Transmits Data
Satellite telemetry enables data transmission from remote systems via satellite networks orbiting the Earth. This technology is particularly crucial for environmental monitoring in remote or inaccessible locations where terrestrial communication networks are unavailable. Two of the most prominent satellite networks used in environmental monitoring are Iridium and GOES (Geostationary Operational Environmental Satellite).
The Iridium satellite network consists of a constellation of 75 (66 active) satellites positioned in low Earth orbit (LEO). The cross-linked network structure provides built-in redundancy and reliable global coverage, even in the polar regions. Additionally, the L-band frequencies (1-2 GHz) it uses for transmission are resilient to adverse weather conditions.
Data transfers from the logger to a satellite and then to the database displayed on a computer or other device.
With these characteristics, Iridium is particularly useful for environmental monitoring in polar and oceanic regions, or any other remote location throughout the globe where cellular networks are not available2.
GOES is a satellite network operated by NOAA (National Oceanic and Atmospheric Administration, United States) that consists of geostationary satellites positioned over the equator. This means that these satellites rotate with the Earth and, thus, provide continuous observation of specific regions.
The network of satellites currently covers over half of the globe from the west coast of Africa to New Zealand between the Arctic and Antarctic Circles. While primarily focused on weather monitoring, forecasting, and disaster management for severe weather events, the GOES network is also used for climate research and environmental observation3.
Although both networks are used to transmit environmental data, they have different use cases. The Iridium network covers the entire globe and may be used for general purpose monitoring by both private companies and public entities.
The Iridium network offers two-way communication, meaning that it can both receive and transmit messages. GOES, on the other hand, is only capable of one-way communication and is used primarily for weather and climate-related applications managed by public organizations and researchers.
Iridium and GOES are two of the more widely used satellite networks for environmental monitoring systems, but others such as Inmarsat, Meteosat, Copernicus, and Argos are also used in some applications. Together, these form a critical component of global telemetry infrastructure, extending the range for real-time data collection beyond areas covered by cellular networks and terrestrial radio systems.
What Is Radio Telemetry?
Radio telemetry involves the wireless transmission of data using radio frequency signals. There are many technologies that fall under this umbrella term, each operating with different frequency bands and protocols. In the context of environmental monitoring, some of the common radio telemetry forms include VHF/UHF, spread spectrum, Wi-Fi, LoRaWAN, and Zigbee.
VHF (Very High Frequency) and UHF (Ultra High Frequency) radio telemetry are traditional forms of radio communication that have been used for decades. VHF and UHF systems operate on narrowband channels licensed by regulatory agencies such as the Federal Communications Commission (FCC) in the United States.
Often used in rural and marine applications, they are generally reliable with good range and resistance to interference since they operate on licensed bands. VHF in particular, with its relatively long wavelengths, propagates well through vegetation and over water surfaces.
Data transfers from the logger to a radio tower and then to the database displayed on a computer or other device.
Spread spectrum radio often uses similar bands to UHF radios like 900 MHz and 2.4 GHz but differs in that it spreads the signal over a wider bandwidth. This helps to reduce interference and increase reliability. It offers moderate range and does not require a license, making it a convenient, cost-effective option for environmental monitoring applications where one or more sites are within line of sight of a base station location.
Wi-Fi is another radio standard that operates in the 2.4 GHz or 5 GHz frequency bands. It has a much shorter range than VHF/UHF and spread spectrum radios, but infrastructure is widely available in urban environments, research stations, and industrial facilities, making it a viable and low-cost option in some applications. Additionally, it supports high data transfer rates that, although not critical in many sensor applications, can facilitate continuous monitoring and higher data throughput including photo and video feeds.
Besides Wi-Fi, several other radio standards have emerged to target the remote sensing and IoT markets. These can be broadly classified as low-power, wide-area networks (LPWAN) intended for power-efficient data acquisition from sensors with low data rates, sometimes operated from batteries.
Platforms and technologies used in this space include LoRa/LoRaWAN (derived from “Long Range”), Sigfox, and Zigbee, amongst others. LPWANs can be established as private wireless sensor networks with dedicated gateways to push data to cloud services, or as a service provided by third parties that maintain infrastructure in a certain area or region.
Some radio protocols allow various network topologies to extend range or create redundancy in a network. Topology refers to the structure and layout of how nodes (remote, radio-equipped sensors in the case of environmental monitoring) in a network communicate with each other. Common types include:
- Point-to-point: In a point-to-point topology, data is transmitted between two distinct nodes. This simple, reliable configuration is applied in situations where direct communication between two specific points is needed, such as a remote monitoring site and a base station.
- Point-to-multipoint (Star): Point-to-multipoint, also known as star topology, is characterized by a central station that communicates directly to two or more remote stations.
- Multipoint-to-multipoint (Mesh): In a multipoint-to-multipoint or mesh topology, each node can communicate with several nearby nodes or every other node in the network, providing multiple pathways for data to reach the central hub or gateway.
In certain cases with extensive sensor networks, other topologies like tree and hybrid configurations can be used. Together, these cover the vast majority of remote environmental monitoring applications.
Alternative Telemetry Methods
While cellular, satellite, and radio account for the vast majority of telemetry applications in environmental monitoring, some applications utilize alternative methods. Examples include inductive modem technology and acoustic transmission. These are most relevant to situations where over-the-air radio signals are not feasible, namely underwater data transmission in the realm of environmental monitoring.
Inductive modem systems utilize a cabled connection but transmit data using electromagnetic induction rather than direct electrical contact. They are commonly used to transmit data to surface buoys from underwater environments.
Inductive modems eliminate the need for direct electrical connections that may pose concerns due to water corrosion and connector maintenance issues. In some cases, buoy mooring systems themselves can serve as inductive cables, simultaneously providing anchoring and a data transmission pathway.
Acoustic telemetry involves the transmission of device data through acoustic (sound) signals. In acoustic systems, a transmitter device receives data directly from a smart sensor or data logger and directs the acoustic signal towards a receiver unit. In many cases, the receiver may relay the data to a traditional over-the-air telemetry system to ultimately deliver it to a cloud data management system.
A common use case for acoustic systems is transfer of data from bottom-mounted platforms in lakes or oceans to a surface buoy where it can be downloaded or relayed. The primary advantage is that it eliminates the need for a long cabled connection that would otherwise be a vulnerable element of the system.
By utilizing these or other alternative telemetry methods, environmental monitoring systems can effectively gather and transmit data in challenging environments where traditional methods are unavailable.
Conclusion
Data telemetry is a fundamental aspect of many environmental monitoring applications. The real-time data acquisition it enables helps to ensure compliance, alert for exceedances and changing conditions, and monitor system health to more efficiently plan maintenance visits.
Between modern radio technology, the widespread availability of cellular networks, and the global presence of satellite networks, remote data acquisition is possible from nearly any location on Earth. Secure, cloud-based systems facilitate data acquisition and management in many applications, but closed private networks can also be configured for added security in applications such as monitoring of critical infrastructure.
Resources
- GSMA. (n.d.). IoT deployment map. Retrieved June 18, 2024, from https://www.gsma.com/solutions-and-impact/technologies/internet-of-things/deployment-map/
- Iridium Communications Inc. (n.d.). The Iridium network. Retrieved June 18, 2024, from https://www.iridium.com/network/
- NASA Science. (n.d.). Geostationary Operational Environmental Satellites (GOES). Retrieved June 18, 2024, from https://science.nasa.gov/mission/goes/