Title: Autonomous Instrumentation for Oceanography

Successful missions at Idukki dam, Kerala

Sensor payloads of Dissolved Oxygen (DO) , Chlorophyll, Turbidity, Temperature, Conductivity were interfaced to a Rabbit Core micro-controller through RS 232 serial ports. The data records of each sensors are stamped with date, time, and GPS values which are transmitted from the MZ 104 main controller. The DO and chlorophyll cum turbidity sensors are mounted on a nose cone. A separate nose accommodates the larger CTD sensor.

The data from these sensors are plotted in Figs.1 and 2. An interesting effect discovered by Maya was an acute oxygen deficiency below 20m. This was validated by measuring DO samples in the laboratory by the Winkler method. It was subsequently confirmed by chemists at NIO who visited Idukki shortly after our trip. The results here are being considered for a high impact publication.

Depth control of the AUV after diving to a set depth.

This major milestone has been completed successfully. It is based on the Linear Quadratic Regulator (LQR). This has been accepted as a paper titled “ Control of the Maya AUV in the vertical and horizontal planes : Theory and Practical results “ to be presented at the 7th IFAC Conference on Maneuvering and Control of Marine Craft scheduled for 20-22 Sept 2006 at Lisbon, Portugal.

Idukki Dam field tests – depth control ( First Mission)

The Idukki Dam waters in Kerala provided the opportunity of testing the AUV at greater depths. This site had a maximum depth of 40m. In this mission, the AUV was commanded to execute a series of staircase dives to increasing depths starting with first staircase to 2m, and ending with a staircase dive to 21m. In the 21m staircase profile, the AUV descended to 2m cruising at this depth for 15s, then to 10m for a shorter time of 5s, then down to 15m again for short time, and finally to 21m for a time of 30s. The ascent from 21m was faster with a brief 5s at 10m, and then quickly up to 0m. The reason for staircase dives was to fully test the depth control of the AUV, and to permit the slower response sensors to fully settle down when cruising at constant depth. The figure below shows the staircase missions.

The staircase dives demonstrate the ability of the Maya AUV to operate in confined spaces. The total span of the staircases in the horizontal direction (time axis) was close to 400m

Data logging of science based sensors at Idukki

Endurance of Maya AUV in Idduki Waters ( 2nd Mission )

The Maya AUV was subjected to two long missions at the Idukki site. In the first mission, Maya nose cone was fitted with oxygen and chlorophyll sensors, and made to complete a rectangular loop of side 560m thrice at a subsurface depth of 1m. The distance covered was ~ 3.5 kms continuous run of 48 minutes.

Two more missions of ~2.0 km each ware also executed with the CTD and Oxygen & Chlorophyll sensor suites. During the middle of each long stretch, the AUV was made to break surface as this confirmed that it was still there, and that the mission was being executed as programmed.

Tests at a Coastal Station in the Arabian Sea

A second set of field tests were carried out on the 22 Nov 2006 at a coastal location (Lat 15° 31.8’N, Long. 73° 13.6’E) off Goa in the Arabian Sea. The maximum depth at this location was 80m. The deployment and retrieval was made from the coastal research vessel Sagar Sukti of the National Institute of Oceanography, Goa. For this test, a CTD nose cone (Fig2 b) was fitted onto front endplate of the hull , and as before the AUV was commanded to dive to different depths in staircase maneuvers. The descent staircase dive to 40m is shown in Fig 4, and the corresponding temperature- depth profile in Fig 5. An inversion layer at 30m was detected by the fast response time (~ 95ms) of the CTD sensor .