Comparisons with other telescopes

Whenever imaging over scales of 0.2'' to 10'' is desired at 31.3 - 45 GHz, there is NO instrument competitive to ALMA, either in existence or planned. Higher resolution will be best done with the VLA. Scales much greater than $\sim 100''$ at 31.3-45 GHz will be best done with a number of instruments: i.e., CARMA heterogeneous array, GBT, and dedicated CMB instruments. Scales larger than 100'' could be done with ALMA in total power and using mosaicking. I am NOT convinced, however, that the total power will work well for extended low brightness continuum emission (eg., Sunyaev Zel'dovich Effect and CMB work). Nevertheless, there is extremely important work for ALMA to contribute here WITHOUT total power measurements. ALMA will be an ideal probe for the high redshift universe. The sensitivity of ALMA in its sweet spot ( $0.2'' - 100'' \leftarrow$ a big range) is simply incredible. MORE ON GBT: The one possible direct competition with ALMA for the angular range of 15'' and larger is the GBT. However, to be competitive a large focal plane array ($\sim$64 elements) at 40 GHz is needed. The single dish radiometers are considerably more complicated and expensive than receivers for an interferometer. The GBT observations will rely on total power measurements, obviously, and thus it is more difficult to reach the low brightness levels. I strongly believe that the interferometric technique is far better. The GBT is also located at a vastly inferior site - atmospheric conditions are likely to severely limit its performance for observations of low surface brightness objects. ALMA outfitted with Band 1 receivers is clearly superior for angular scales up to $\sim 100''$. The GBT, however, may be an ideal way to recover short baseline information.