Peering into the Future: How Dual-Frequency Satellite Receivers Will Democratize Land Surveying

Blog Post
March 23, 2017

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Drawing Lines

Across the developing world nearly a billion people live without legal title to their land. In order to formalize this property, governments need to issue deeds and create registries in which to record them. But unlike other types of property, parcels of land cannot be registered until they have been defined. Delineating one person’s property from another’s is a serious technical challenge and a prerequisite for granting secure legal titles.

Precise surveying is expensive, requiring specialized equipment operated by professional surveyors. This means that precision is often inaccessible to people in the marginalized populations who most require it.

When professional surveyors are asked to compromise on price, the accuracy of the service they provide also becomes subject to compromise. Walter Volkmann, a third-generation land surveyor and president of Micro Aerial Projects L.L.C., saw firsthand how one such negotiation combined with the politics of apartheid to jeopardize formalization efforts in Namibia in the 1980s:

“In the late 1970s South Africa decided to no longer rule Namibia, formerly known as South West Africa, as a fifth South African province. Instead it began to follow a policy in terms of which Namibia would gradually be granted administrative autonomy until it would ultimately gain full independence from South Africa. In 1978 the first “one man, one vote” elections were held. Although boycotted by SWAPO, a major anti-apartheid movement, the newly elected “Government of National Unity” decided to extend the right to formally own land in the then racially segregated urban areas to all people, irrespective of skin color. For this purpose, the so-called “locations”, townships which were developed and reserved exclusively for the housing of non-white citizens under South African apartheid policy, had to be surveyed and registered in the Deeds Registry. My entry into the land surveying profession fell into that period in the early 1980’s when the large volume cadastral surveys of the so-called “locations” were being rolled out. While the small number of professional land surveyors were welcoming this sudden abundance of work, the government was of course facing the challenge of funding these surveys. And, as so often happens when budgets are being discussed for survey work, an attempt was made to negotiate a reduction in fees in exchange for a relaxation in the prescribed accuracy standards. Given the prevailing technology at that time, accuracy standards were indeed a legitimate factor in the cost of cadastral surveying. One could argue that lower fees would result in the survey of a larger number of properties and thereby facilitate formal ownership for more people than would otherwise have been the case. However, this would result in the absurd reality that although formal ownership of land would be made possible for all citizens irrespective of race, an ugly residual of racial prejudice would remain: your skin color would determine the accuracy to which your property was surveyed and thus the security of your title. In the end both parties agreed on reduced fees for the survey of formerly “black townships” without compromising accuracy standards. Although the introduction of the term “black township” in the text of the cadastral survey legislation is not exactly indiscriminate, it certainly is less detrimental and offensive than granting inferior security of title to formerly disadvantaged citizens. And, rather happily, the discriminatory language has long since vanished from the regulatory texts as now all formal townships in Namibia enjoy a homogeneous standard of accuracy and hence security of title.”

Subsequent advances in Global Navigation Satellite System (GNSS) technology have weakened the correlation between precision and cost, but survey-grade accuracy is not yet widely and cheaply available.

Widespread access to this level of accuracy is critical for formalization efforts because expense is not the only problem with depending on professional surveyors to document the world’s informal property. There is a more fundamental problem of scale. A significant percentage of all land in the developing world is informally owned. There is simply not enough time for professional surveyors to register it all.

According to the Cadasta Foundation, there are fewer than two professional surveyors per 10,000 square kilometers of land in the Ivory Coast and Tanzania, compared to 41 per 10,000 square kilometers in the United States.

There were only 74 registered land surveyors in Uganda in 2015 and an estimated 15 million parcels of informally owned land. With more than 200,000 parcels per registered surveyor, Cadasta calculates that it would take them over a thousand years to finish the job.

When everyone has access to survey-grade precision, formalization efforts can be expanded and accelerated. With the advent of relatively cheap, dual-frequency satellite receivers, this may soon become possible.

Dual-frequency receivers

Position measurements using a single frequency are vulnerable to interference and accurate, at best, to about 5 meters. This is fine for most people’s daily use, and in developed areas wifi signals can be used to augment accuracy. All smartphones, for example, use single-frequency receivers. But errors on the scale of meters are not good enough for survey work, which should be accurate to the 1-10cm range, depending on local standards and the type of survey.

By making use of a second signal frequency, dual-frequency receivers can correct for delays caused by the ionosphere, which are the greatest single contributor to inaccuracy. Using a second frequency also provides greater signal redundancy, allowing for better error-correction and improved satellite availability in tree cover and urban canyons. With error-checking algorithms that can identify faulty satellite signals, dual-frequency receivers produce measurements that are not only accurate but trustworthy. This last property is important when it comes to registering land, as it allows the authorities validating title claims to have confidence in the integrity of the data they are given. Dual-frequency receivers also resolve positions more quickly than single-frequency receivers, so the surveyor does not have to wait as long on a reference point acquiring multiple satellites.

Using free, open-source signal processing software, dual-frequency receivers can achieve survey-grade accuracy. The downside of dual-frequency receivers is the cost of the hardware. In 2013 a $2,500 dual-frequency receiver could be described as “incredibly inexpensive.”

Two things need to happen in order for hardware prices to continue to drop: the deployment of large numbers of satellites operating civilian signals on at least two different frequencies, and a large, competitive market for survey-grade receivers. It appears that both of these conditions will be met in the near future.

Open Signals

When the USA launched the first navigational satellite constellation, GPS, it broadcast signals on two main frequencies. The first signal, called L1 (1575.42 MHz), was intentionally degraded, limiting the accuracy of the single-frequency receivers that used it to around 100m. The second signal, L2 (1227.60MHz), was available only to authorized users, like the US military, who were issued encryption keys. This policy prevented civilians and foreign governments alike from getting precise GPS coordinates without ground-based augmentation systems. This policy was eventually reversed, but not before a few civilian companies figured out how to use the L2 signal without an encryption key and patented the techniques. Until a second civilian signal becomes available to replace L2, these patents will continue to restrict competition in the development of dual-frequency receivers.

In 2013 the governments of the United States and the United Kingdom announced their commitment to “ensuring that GPS civil signals will remain perpetually free and openly available for users worldwide,” agreeing to place all technical information and intellectual property relating to civil GPS signals in the public domain. Manufacturers will be able to patent specific receiver designs, but not techniques needed to track the signals themselves, like the patents filed on the L2 signal. A US Department of State document from September 2013 notes that this commitment to open signals is intended in part to promote “open, market-driven competition” and “equal access for user equipment manufacturing.”

One of these new, open signals, the L5 (1176.45 MHz) signal, is the best candidate to replace L2 for dual-frequency use. L5 is the most advanced civilian signal, designed for “safety-of-life transportation and other high-performance applications.” An open GPS signal called L2C (1227 MHz) is being introduced to replace the L2 signal, but it will be used by fewer satellites and the US Government may not continue to support it once the L5 constellation is complete. Survey-grade receivers need to be able to see at least eight satellites to function optimally, making the L5 signal, which is more powerful than L2C and will be used by multiple satellite constellations, a better option. A modernized American GPS constellation broadcasting both L1 and L5 from its newer IIF and Block III satellites is scheduled to be completed by 2024. The European Union’s Galileo constellation is deploying satellites with the interoperable E5 signal, meaning that a full complement of 24 L5/E5 satellites will be available before either constellation is completed individually. Multi-constellation receivers that can also use Russia’s GLONASS and China’s BeiDou satellites in addition to GPS and Galileo could eventually have access to more than 100 satellites.

New Markets

Recent technological advances are creating huge new markets for accurate GNSS receivers.

Autonomous vehicles, from tractors, to taxis are poised for massive growth and will require more accurate and reliable GNSS receivers for both functionality and safety purposes. Single-frequency receivers can also achieve very high accuracy with augmentation, but the inherent accuracy and integrity offered by dual-frequency receivers makes them more attractive for safety applications.

Aerial drones, used for everything from oil and gas exploration to grocery delivery, will benefit from increased accuracy in vertical positioning.

Commercial aircraft will be able to use dual-frequency L1/L5 receivers for navigation and safety-of-life applications.

The average smartphone user will appreciate more accurate location services for navigation, fitness apps, even virtual reality.

Manufacturers are already developing dual-frequency receivers for these markets. Broadcom, for example, which manufactures GNSS chips for smartphone giants like Apple and Samsung, revealed in 2016 that it was testing a dual-frequency chip for cell phones.

Future Developments

Survey-grade GNSS receivers will continue to shrink, become cheaper, and may eventually be digitized altogether. A Software Defined Receiver (SDR) like the Trimble Catalyst can transform an android phone into a dual-frequency receiver with a software download and a plug-in antenna. The Catalyst requires a monthly subscription to Trimble’s augmentation services and accuracy is pay-as-you-go, with meter accuracy priced at $40 per month, and centimeter precision at $350 per month.

But devices with open-source SDR and post-processing software could reduce the total user cost to the price of the antenna. As long as it had enough processing power, an SDR device could be updated to support additional constellations and signals without any hardware development costs.

Antennas for surveying receivers currently cost a few hundred dollars and are fairly large. They must be shielded from reflected signals, especially those bouncing off the ground, and usually have a plate around 10cm in diameter built into the bottom of the antenna.

New methods of compensating mathematically for these reflected signals promise survey-grade precision with antennas small enough to fit in a smartphone. A team at the University of Texas, working with Samsung, is using these techniques to achieve centimeter precision with $5 antennas similar to those currently found in smartphones. They estimate that their system, consisting of an SDR and antenna, will “eventually cost less than $50.”

The hardware component of the Trimble Catalyst, introduced in November 2016, costs $350, seven times less than the “incredibly inexpensive” X90-OPUS introduced in 2013. With increased competition among manufacturers and increased demand, prices will only continue to drop. It is hard to predict how far, but the fact that a major chip-maker like Broadcom is experimenting with dual-frequency chips in cellphones is telling. Apple is unlikely to accept adding hundreds of dollars to the price of an iPhone for a dual-frequency receiver and antenna.

What Will This Mean for the Various Stakeholders in Property Formalization Efforts?

For governments and aid agencies, it will be easier and cheaper to organize large-scale formalization efforts when surveying is decentralized and pushed down to the local level. The government’s focus will move to providing the legal staff and registry system needed to validate and record property claims.

Crowd-sourced surveying will allow more property to be registered more quickly. The more complete a land registry is, the more useful it is to government officials managing land use, natural resources, and public utilities.

NGOs will also be able to expand their formalization programs thanks to reduced equipment and personnel costs. As data collection becomes easier and cheaper, they may dedicate more resources to addressing governance issues and bureaucratic obstacles that threaten to negate the positive effects of formalization.

Occupants will benefit the most from the democratization of surveying. In areas where the nature of customary ownership or usage does not translate easily into a formal cadastral system (as with shared lands with communal rights or lands used by different parties according to an annual cycle) land use arrangements decided at the local level are preferable.

Cheaper surveying should allow for the reduction of property registration fees, which currently discourage many small landowners from participating in formalization programs. According to the World Bank, registering property in Sub-Saharan Africa costs, on average, 8 percent of the value of the registered property.

For professional surveyors, documenting informal property is time-consuming and not especially profitable. When the task of data collection is crowdsourced, they will be free to focus on more demanding work which requires expertise in managing and analyzing geospatial data. This will include designing and supervising crowdsourced data collection projects.

Note (March 27, 2017)—This post has been updated with additional information about open satellite signals and equipment prices. Reference to a World Bank report from 2005, which put the average cost of registering land in Sub-Saharan Africa at 14.4 percent of property value, has been replaced with 2016 World Bank data which gives an average cost of 8 percent.

Related Topics
Global Land and Property Rights