#### System temperature

We start by deriving the sky temperature with:

| (52)

Estimating requires knowledge of the forward efficiency . It is also used to compute the sky emission :

| (53)

The water vapor content variable of an atmospheric model predicting sky brightness ( and ) and opacity ( and ) in the signal and image sideband is then varied in order to minimize the following quantity:

| (54)

The system temperatures for the signal and image sidebands are then computed as follows:

|  |  | (55)
|  |  | (56)

where:

| (57)