Technical Notes & Environmental Science
Precision Sonar Lake Monitoring
Mapping hydro-physical spatial distributions, sediment layers, and subaqueous fish stock populations using high-resolution CHIRP sonar, centimetre-precision GNSS positioning, and tethered ROV bio-monitoring in Bhimtal and Naukuchiatal.
1. Centimetre-Precision Hydrographic Surveys
Methodology of subaqueous mapping in Naukuchiatal and Bhimtal
Traditional bathymetric measurements in inland waterbodies often rely on grid-less hand-held lead-line soundings, which offer low spatial resolution and miss critical subaqueous structures. In this pilot project, the proposer deployed survey-grade, centimetre-precision **Global Navigation Satellite System (GNSS)** positioning data integrated with high-resolution Down-Imaging sonar.
Operating from a manually propelled canoe to prevent local chemical pollution, turbid disturbance of bottom sediments, and underwater acoustic noise, the canoe traversed Naukuchiatal and Bhimtal lakes in an exhaustive, high-density **zig-zag track pattern**. The logging system gathered Compressed High Intensity Radar Pulse (**CHIRP**) dual-spectrum sonar returns, automatically linking hydro-acoustic backscatter data directly with precise GPS timestamps.
2. Subaqueous Fish Stock & Target Strength Monitoring
Estimating fish populations non-invasively via active sonar scans
Standard methods for studying coldwater fish populations (like the endangered *Tor putitora* or Golden Mahseer) rely on sweep netting, beacons, or human divers. These traditional approaches are geographically limited, highly intrusive, and can cause significant harm to vulnerable aquatic biodiversity.
Our non-invasive active hydroacoustic surveys capture localized multi-beam side-sonar scans to estimate fish populations and study feeding, schooling, and distribution behaviors. Raw echo returns measure acoustic **Target Strength (TS)**, which is directly proportional to the physical size of the fish and the volume of its swim bladder. The backscatter cross-section is computed as:
Where:
- TS = Target Strength in decibels
- σ_bs = Acoustic backscattering cross-section (m²)
Using these calibrated algorithms, sonar returns are processed on desktop GIS software to differentiate between schooling exotic carps (Grass, Silver, Common Carp) and native coldwater species in the winter layers of Nainital lake.
3. Tethered ROV Subaqueous Bio-monitoring
Non-disruptive, near-bottom water quality and sediment logging
To evaluate deep lake layers safely, we piloted subaqueous data acquisition using a tethered **Remote Operated Vehicle (ROV)**. This self-contained, micro-thruster system allows the team to perform underwater inspections in Naukuchiatal and Bhimtal without disturbing soil stratigraphy or benthic biodiversity.
The ROV platform acts as a mobile sensory station, carrying high-resolution cameras and environmental sensors directly into deep coldwater layers to measure dissolved oxygen levels, bottom soil hardness, and algal bloom distributions.
| Tethered ROV Platform Specifications (PowerRay Wizard) | |
|---|---|
| Operating Depth Rating | Maximum 30 meters (98 feet) |
| Locomotion & Control | 3 Thrusters (2 horizontal, 1 vertical) with manual/auto pitch stability |
| Max Speed | 3 Knots (1.5 meters per second) in standing water |
| Battery Power | 94.72 Wh Lithium-Polymer (14.8V, 6400 mAh) |
| Lighting System | Dual 450-lumen dimmable LED lamps |
| Camera System | 1/2.3-inch CMOS, 12 Megapixel camera sensor |
4. Limnological Analysis & Spectrometry
Dissolved oxygen titration and FT-UV Vis spectrometry protocols
To ensure accurate water quality baselines, near-surface and deep water samples were systematically gathered. Dissolved Oxygen (DO) was tested using a chemical titration kit from Aquasol, which was validated and cross-calibrated against a high-precision digital probe at the **ICAR-Directorate of Coldwater Fisheries Research (DCFR)** in Bhimtal.
Furthermore, our laboratory utilizes a single-beam **Fourier Transform UltraViolet-visible (FT-UV Vis) Spectrometer** for direct chemical analysis:
- Nitrate & Nitrite Estimation: Measured directly from water samples placed in quartz cuvettes using UV absorbance bands.
- Ammonium Estimation: Estimated spectrophotometrically following chemical oxidation with potassium peroxodisulphate. }