GLT Antenna Surface Improvement
Improvement of the accuracy of the GLT antenna dish surface is done by the photogrammetry.
The photogrammetry method is to put reflective targets on the dish surface, taking pictures with flash light, analyze the relative positions of the targets, and calculate the surface accuracy. In the summer of 2018, we performed the first photogrammetry measurements. The first photogrammetry map shows a saddle-like structure with the overall surface accuracy of 180 micron (left figure). This is very far from the measured value at the hanger of 40 micron before we lifted the surface to the antenna mount. The red circles in the left figure are the points we put ropes for lifting the dish on the antenna mount, so this large deformation was probably caused by lifting the dish. After several times of iteration of the photogrammetry and the panel adjustment, we could reach to the surface accuracy of 21 micron (right figure), which is good enough for the 230 GHz and 345 GHz observations.