CORS Makes Inroads Into Private Sector

42 REPORT

CORS Makes Inroads Into Private Sector

Instead of using the traditional base station and radio to send correction data to a rover, a Continuously Operating Reference Station (CORS) provides unmatched precise positioning with respect to a reference point that empowers multiple sectors. A CORS network stores data, in some circumstances processes it, and then transmits this data to rover receivers. By Priya Chadha

Since the National Oceanic and Atmospheric Administration (NOAA), the apex regulatory agency in the US, built a network of Real-Time Kinematic (RTK) base stations to augment positional accuracy provided by the Global Positioning System (GPS), many countries and private agencies have followed suit by establishing a Continuously Operating Reference Station (CORS) network. Unfortunately, India did not have such a network in place until very recently, even as other developing countries jumped onto the bandwagon. That has now changed as the Survey of India (SoI) is offering the facility to the private sector for free. At present, SoI has CORS facilities in place in 81 locations.

About CORS

CORS collects and records Global Navigation Satellite System (GNSS) data from a given location for relative positioning. It provides a high-precision platform for surveying, mapping and monitoring large infrastructure projects like irrigation, railroad, canals, dams, smart cities, and drainage planning, besides enabling better management of revenue maps and state boundaries. The data is then streamed to a master control center for better control and monitoring, with one redundant control station (that serves as backup) for uninterrupted service in case maintenance is needed, or if there is a requirement for updating data centre and communication.

“In the first phase, we introduced the service for internal users; in the second, for government organizations; and in the third, our focus was the industry (private sector),” said Neeraj

Gurjar, Director, Geodetic & Research Branch, Survey of

India, to Geospatial Artha.

The move has cheered all stakeholders and will add teeth to the geospatial industry. CORS has unmatched ability to provide precise positioning — a well-established network can allow users to obtain accuracies in the order of centimeters. This accurate location of an object with respect to a reference point empowers multiple sectors and with ever-increasing connectivity and digitalization, its utility will rapidly expand.

CORS has a fault-tolerant ability that makes it the most sought after mechanism for geophysical survey. It is also affordable, accurate, reliable, and saves time.

At present, CORS is functional in Haryana, Karnataka, Maharashtra, NCR, Uttar Pradesh and Uttarakhand, enabling accurate geopositioning infrastructure and real-time data acquisition. Other states where the network is expected to be operational within the next two months are Madhya Pradesh, Rajasthan, Punjab and Himachal Pradesh. Those left out will get the facility within six months.

“CORS enables a user to do relative positioning without operating the base station, by depending on that role being fulfilled by the network’s reference stations. While the GNSS work can be supported by a reference station, it usually involves more than one field receiver. But CORS does not need two receivers, which means a user can collect data in the field with a single GPS receiver, send it to the nearby reference station, and later retrieve the data,” Gurjar went on to add.

“Usually, users can subscribe to the CORS network on a monthly or yearly basis to receive Network Real Time Kinematic (NRTK) corrections with their rover, instead of having to set up their own base station. But this time, they will be able to avail it for free for three months,” he elaborated.

The network ambiguity resolution should be conducted within a single observation epoch, which means in real time. Hence, the CORS network. But there are certain ambiguities that need to be worked on.

Advantages of CORS

CORS has a fault-tolerant ability that makes it the most sought after mechanism for geophysical surveys. It is also affordable, accurate, reliable, and saves time. Another advantage is that

CORS enables a user to do relative positioning without operating the base station, by depending on that role being fulfilled by the network’s reference stations.

it works without expensive data radios to broad RTK positioning. A CORS network of reference stations will be established, which provides a Virtual Reference Station (VRS), allowing users to access long-range high-accuracy corrections.

On the advantages of the facility in boosting the industrial sector, Amit Saxena, Regional

Sales Manager (India & SAARC)-

Geospatial, Trimble, said, “Be it land management projects or transportation, particularly railways and roads, the CORS network provides a precise positioning platform for mapping and monitoring large infrastructure projects. With the CORS network in place, the staff of the hosting facility does not have to be confined to a particular area and can be sent to multiple locations, thus cutting down on time and maximizing efficiency.”

Beneficiaries of CORS

Surveyors, GIS users, engineers, scientists, and the public at large that collect GPS data can use CORS data to improve the precision of their positions. CORS-enhanced post-processed coordinates approach a few centimeters relative to the National Spatial Reference System, both horizontally and vertically. While CORS can be configured to support differential GNSS (DGPS) and RTK applications, as in Real-Time Networks, most networks constantly collect GNSS tracking data from known positions and archive the observations for

subsequent download by users from the internet.

The major obstacle lies in cutting down the convergence time, which is imperative to resolve the integer carrier phase ambiguities between the network’s reference stations. Once these are resolved, the network is able to provide precise corrections of the atmospheric (ionospheric and tropospheric) delays between the reference stations. Subsequently, these accurate estimates are used to predict the differential atmospheric delays at the approximate location of a user, enabling him to obtain high-precision positions while applying these atmospheric corrections.

Towards self-reliance

In India, the CORS network makes use of NavIC receivers for high-precision positioning, translating into reducued dependence on foreign satellite systems and increased self-reliance. The development of CORS applications for the Indian context was an amalgamated effort by the Council of Scientific and Industrial Research (CSIR), various academic institutions, ISRO (Indian Space Research Organisation) and SoI. The new shift in the outlook towards geospatial and data policies in India signals greater collaboration among public and private entities, ensuring widespread adoption of CORS for various applications, and a strategy that ensures commercial success as well as the realization of larger public interest.