Changes In T$_{sys}$ With Elevation (T$_{spill}$)

Spillover can double T$_{sys}$ at L-band when observing sources at low elevation. Since data obtained at lower elevations will therefore be noisier, the observer may wish to down-weight them relative to the parts of the run at which the object under study was at higher elevations. Unfortunately, there is no easy way to do this in AIPS; the task WTMOD offers only limited flexibility to modifying weights. The best option is to avoid observing below elevations of about 30$^{\circ}$. Some objects, such as the Galactic center, never reach high elevations. For those situations one has to take the higher system temperature into account when estimating the rms noise which one aims to achieve.