Why This Matters Right Now

The Ministry of Defence recently signed a ₹449 crore contract with Bengaluru-based Accord Software and Systems Private Limited (ASSPL) to supply 20 Enhanced Capability GNSS Jammers to the Indian Navy. The stated purpose is defensive — disrupting enemy missiles and drones — but the procurement puts a spotlight on something field surveyors in India rarely think about until it bites them mid-campaign: GNSS signal interference is real, it is growing, and RTK and PPK workflows are particularly vulnerable to it.

This article is not about military electronics. It is about what a survey team running an RTK base-rover setup or a UAV-PPK mission needs to understand when jamming or spoofing degrades their fix quality — and what actually helps in the field.

What Exactly Is GNSS Jamming, and How Is It Different from Spoofing?

Illustrative: RTK base station field setup. "20220831-OSEC-LSC-0083" by USDAgov is marked with Public Domain Mark 1.0. To view the terms, visit https://creativecommons.org/publicdomain/mark/1.0/.

Jamming floods the radio-frequency environment with noise on the same frequencies that GNSS satellites use (L1, L2, L5, etc.). The receiver cannot distinguish the satellite signal from the noise, so it either loses lock entirely or degrades to a float or single-point solution. According to Septentrio's interference documentation, a single illegal chirp jammer — the kind truckers sometimes use to avoid toll tracking — can disrupt GNSS signals within a 400-metre radius, affecting surveying, construction, marine navigation, and drone operations.

Spoofing is subtler and more dangerous for precision work. A spoofer transmits counterfeit GNSS signals that the receiver accepts as genuine, producing a position that looks valid but is wrong. U-blox's field testing notes describe how spoofing can cause the receiver to report a confident fix at a location that is entirely fabricated — no warning flags, no elevated DOP values.

For RTK surveyors, the distinction matters because:

• Jamming is usually detectable (loss of fix, high noise-on-signal metrics, sudden float).
• Spoofing can silently corrupt your dataset with no obvious field indicator.

How Jamming Specifically Breaks RTK

RTK depends on resolving carrier-phase ambiguities between the base and rover. This requires a continuous, clean phase lock on multiple satellites. When interference enters the picture, several failure modes cascade:

1. Cycle slips — the receiver momentarily loses phase lock and re-acquires with an integer offset. Every cycle slip resets ambiguity resolution.
2. Reduced satellite count — if the jammer is strong enough, the receiver drops satellites below the minimum needed for a fixed solution (typically 5+ for RTK).
3. Elevated noise on carrier phase — even without full loss of lock, elevated noise inflates position uncertainty. A receiver that reports "fixed" may still carry centimetre-level errors that exceed your project tolerance.
4. Phase offsets under array-based mitigation — research published in NAVIGATION: Journal of the Institute of Navigation specifically addresses this: antenna arrays used for interference mitigation introduce carrier-phase offsets that must be compensated before RTK ambiguity resolution can succeed.

A 2025 study published in the Journal of Navigation on a continuously operating reference station (CORS) subjected to prolonged jamming found significant deterioration in positioning accuracy even when the receiver maintained some level of signal tracking. The implication for field teams: your receiver staying "on" does not mean your data is usable.

Worked Example: Spotting a Jamming Event in Your RTK Log

Illustrative: GNSS receiver signal loss display. "SiGe GN3S Sampler v3" by SparkFunElectronics is licensed under CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/.

Suppose you are running a cadastral survey in a peri-urban area near a logistics hub. Your base is set up on a known control point; the rover is collecting boundary marks. Midway through the session, you notice:

• Fix status drops from Fixed → Float → Single over about 90 seconds.
• The number of tracked satellites falls from 14 to 6.
• Signal-to-noise ratio (SNR/C/N₀) values drop across multiple constellations simultaneously (GPS, NavIC, GLONASS all affected at once).
• After the event, the receiver re-acquires a fix, but the baseline residuals are elevated compared to the morning session.

The simultaneous multi-constellation SNR drop is the key diagnostic. Multipath typically affects individual satellites based on geometry; a jammer hits all of them at once. If you see this pattern in your receiver's observation log, flag every epoch from roughly 60 seconds before the drop to 120 seconds after re-acquisition. Do not use those points without independent verification.

What Mitigation Steps Actually Work in the Field?

Before the Campaign

• Check for known interference sources. Logistics parks, toll plazas, and military exercise zones are common jammer hotspots in India. Plan your base station location away from these if possible.
• Use a multi-constellation, multi-frequency receiver. A receiver tracking GPS L1/L2/L5, NavIC L5/S, GLONASS, and Galileo is harder to jam completely than a single-constellation unit. Jamming all bands simultaneously requires significantly more power.
• Enable interference detection logging. Most professional receivers (Septentrio, NovAtel, Trimble) have built-in RF spectrum monitoring. Turn it on and log it — it gives you post-hoc evidence of interference events.

In the Field

• Monitor fix quality metrics continuously, not just at collection time. Watch C/N₀ per satellite, PDOP, and the fixed/float status indicator.
• Raise your antenna. Ground-based jammers are low-power. Even a 1.5 m survey pole versus a vehicle-mounted antenna can meaningfully change your signal environment.
• Use a ground plane or choke-ring antenna where budget allows. NovAtel's multipath documentation notes that choke-ring designs attenuate low-elevation signals — the same geometry exploited by ground-based jammers.
• Switch to PPK if RTK becomes unreliable. Log raw observations at both base and rover. If a jamming event corrupts the real-time link, you can reprocess in the office with a cleaner baseline, masking the affected epochs.

Post-Processing

• Inspect residuals epoch by epoch. Software like RTKLIB, Leica Infinity, or Trimble Business Center will show you carrier-phase residuals. Anomalous spikes correlate with interference events.
• Cross-check against NavIC. India's own regional navigation system operates on L5 and S-band. If your receiver supports NavIC and your GPS/GLONASS data looks corrupted but NavIC looks clean, that asymmetry helps you identify which epochs are trustworthy.
• Apply independent control. For any survey where you suspect interference, close your traverse or check your GCPs against independently surveyed points. Spoofing in particular will not show up in residuals if the entire session was affected.

The Bigger Picture for Indian Surveyors

The Navy's jammer procurement is a reminder that India's electromagnetic environment is becoming more complex, not less. Military exercises, border zone operations, and even civilian anti-drone deployments all generate RF environments that can affect survey-grade receivers. GPS World's research roundup on jamming and spoofing notes that new GNSS applications increasingly demand resilience against radio frequency interference — a requirement that is moving from defence into mainstream precision positioning.

For field teams, the practical response is not panic but preparation: log everything, understand your receiver's interference indicators, design your campaign with redundancy, and treat any anomalous fix-quality event as a data-quality flag until proven otherwise. NavIC's growing constellation is an underused asset here — push your receiver vendor to confirm full NavIC support and make sure it is enabled.

The ₹449 crore deal will put 20 high-capability jammers into Indian naval service. Your RTK base station will not be the target. But the broader proliferation of jamming technology — military and civilian — means the skills to detect and respond to interference are no longer optional for serious field surveyors.

References

• Indian Navy to Get Enhanced Capability GNSS Jammers in Rs 449 Crore Deal — Devdiscourse
• Indian Navy Gets 20 Advanced GNSS Jammers — Indian Masterminds
• Effects of Prolonged GNSS Jamming on a Continuously Operating Reference Station — Taylor & Francis / Journal of Navigation (2025)
• Combat GPS/GNSS Interference — Septentrio
• Enabling RTK Positioning Under Jamming — NAVIGATION: Journal of the ION
• GNSS/GPS Jamming and Spoofing Tests Under Actual Conditions — U-blox
• Understanding and Mitigating GNSS Multipath Interference — NovAtel
• Research Roundup: Combating Jamming and Spoofing — GPS World

Researched with AI assistance and reviewed by Jannat Khosla.

Hero image: "Leksand SWEPOS reference station" by Johan G is licensed under CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/.