display | more...
Since the main reflector for the Arecibo Observatory telescope (all 70,000 square meters of it) is actually made up of thousands of individual panels, its shape slowly warps over time and it must be resurfaced. Scientists recently conducted a survey to resurface the dish, using the technique of photogrammetry.

In order to conduct the survey, a small retroreflecting strip was placed on the corner of each panel. Surveyers then took multiple images from up on top of the platform, and from the top of one of the towers, at night using a powerful flash. The resulting images picked up almost exclusively on the points of light produced from the flash reflecting off of the retroreflectors. Unfortunately, the dish is so large that scientists were forced to interpolate among the different images to put together a complete image of the entire dish. Using their knowledge of where each of the points where the retroreflectors were located, they were able to calculate the precise curvature of the dish, and from there went about deciding which panels needed to be adjusted to restore proper curvature. Crews of workers then descended under the dish to manual adjust the screws on each panel which had slipped out of alignment.

The main difficulties involved in this project related first to the longevity of the retroreflectors. In the tropical climate of Puerto Rico, they were only expected to last a few months at best, meaning the survey had to be completed, the data interpreted, the adjustments made, and a follow-up survey conducted all within that short time-frame. Second, the cameras required for the survey were incredibly large and bulky, making it difficult to get them up to the top of the platform or onto the towers. While smaller digital cameras provided decent results, the pixelated nature of the images obtained reduced the precision with which the calculations could be made.

Log in or register to write something here or to contact authors.