Daishsat specialise in precision GPS and ground geophysical surveys. Click on the links below to see what we do and how we do it. GRAVITY | GPS | PROCESSING & IMAGING GPS GRAVITY SURVEYS Gravity surveys have been carried out to estimate mass distributions within the earth for over 100 years. The real limiting factor in the widespread utilisation of the method was that each gravity station's level must be surveyed accurately. Most of the common gravity meters in use can obtain the gravity readings to a resolution of 0.01 mGal, which equates to a required resolution in height of 3cm. Previously, this level of precision was only obtainable by conventional spirit levelling. This made it expensive and time consuming and only utilised on small-scale detail surveys. On regional surveys, barometers (1-5m height accuracy) were used in Australia for many years while Inertial Navigation Systems (INS) have also been utilised on occasions. GPS has revolutionized the positioning and navigation industries around the globe and made 5cm positions and levels easily and reliably obtained for gravity surveys. This has lowered the cost of acquisition and greatly increased the utilisation of gravity as an exploration and evaluation tool. Gravity Survey Uses Geological Mapping - Used on a regional scale for mapping the subsurface geology Petroleum Exploration - Used on a regional scale for mapping sedimentary basins Coal Exploration - Mapping of coal beds within sedimentary basins Mineral Exploration - Reconnaissance and direct indication of deposits Geotechnical Studies - Mapping subsurface cavities Environmental Studies - Mapping of groundwater Regional, Detailed and Microgravity Surveys Daishsat specializes in conducting high quality gravity surveys for clients in the mining, exploration, and environmental industries. The company can offer a range of positioning and surveying solutions to compliment the gravity data acquisition. The company own and operate Scintrex CG-3MH (Micrograv) gravity meters, Leica, Ashtech and Trimble GPS receivers and Leica terrestrial optical survey instruments. The company can complete the planning, acquisition, processing and interpretation of gravity surveys using a variety of techniques in all types of terrain.   Heliborne Gravity In heliborne operations, the crew usually consists of the helicopter pilot and the gravity surveyor, who is responsible for both the gravity and GPS observations. The usual procedure is for the pilot to navigate to the proposed survey station and land in a clear flat spot. The gravity surveyor will then exit the aircraft and take a gravity reading as close as possible to the GPS sensor, which is generally mounted on the rear of the helicopter. Using kinematic GPS techniques and P-code GPS receivers, positions and levels of the gravity station can be resolved to better than 5cm while the reading resolution of the Scintrex CG-3MH is around one 0.01 mGal. Production rates of the heliborne crew can be up to 60 to 70 stations per day, depending on the station spacing and terrain type. This makes it a cost effective method for large scale regional surveys were vehicle access is impractical or in rugged mountain areas where other types of access would be impossible. Vehicle-borne Gravity In regional gravity surveys completed by 4wd vehicles, the surveys are usually completed using a two man crew, one driver/navigator and one gravity surveyor. Surveys can sometimes be completed with one person who drives and completes the acquisition, but for safety and production reasons we often use a two-person crew. During vehicle operations, gravity acquisition is conducted concurrently with GPS observations. As with the heliborne operations, P-Code dual frequency GPS receivers are used for the surveying and Scintrex CG-3MH gravity meters are used for the gravity observations. Similar to the heliborne work, using kinematic GPS techniques and P-code GPS receivers, positions and levels of the gravity station can be resolved to better than 5cm while the reading resolution of the Scintrex CG-3MH is around 0.01 mGal. Production rates of the vehicle crew can be up to 120 stations per day, depending on the station spacing and terrain type. Detailed Gravity Surveys by Foot On surveys where the station spacing is very short, say 10 to 50m, or the terrain is too rugged for vehicles, then the gravity survey can be conducted on foot. Generally this is completed using a two-person crew, one completing the GPS observations with the other conducting the gravity acquisition. For the surveying, Leica SR9500 RTK GPS receivers are used to provide positions and levels on each gravity station to an accuracy of 20mm or better. Production rates can be up to 150 stations per day depending on access and terrain. Microgravity In microgravity, the station spacing is very short, say 1 to 2 meters. In these surveys both the gravity and levelling must be rigorously surveyed. The company use a combination of RTK GPS and traditional conventional surveying equipment to survey the levels of all gravity stations to better than 5mm. Daishsat owns and operates the Scintrex CG-3MH, a gravity meter specially designed for microgravity surveys. It has a reading resolution of 0.001 mGal and a standard deviation in field use of 0.005 mGal. Special field techniques must be utilised to reliably obtain this level of accuracy.