First Year Performance Paper - Section 2.3.2
2.3.2 The In-Ice Configuration
String-21 consists of a 2540 meter cable, 60 DOMs, pressure sensors, thermistors, and a dust logger to measure the optical properties of ice throughout the deployment , as shown schematically in Fig. 3. The 60 DOMs are spaced 17 meters apart on the deepest 1000 meters of the string.
The actual depth of the deepest DOM on the string (2435 m) was determined with data from the two high-resolution pressure sensors, spaced 1000 m apart, together with a laser survey of the distance from the surface to the water level in the borehole. The pressure reading from the deeper pressure sensor, located just above the next-to-deepest DOM, provided the absolute depth of the string, which is defined as the depth of the deepest DOM. The pressure was corrected for the compressibility of the water in the hole, which was measured with data from both pressure sensors by requiring that the difference in depth reading be independent of depth and in agreement with the nominal spacing of the sensors (except for a small difference due to cable stretching). The coordinates of the DOMs higher up the string were then determined by adding the vertical spacing between modules, which were measured during deployment with a laser ranger. Depths of individual DOMs are determined to an accuracy of 50 cm.