# Interpolation of calibration products

MRTCAL computes one set of calibration products per chunk. These products are:

- the receiver temperature,
- the calibration temperature,
- the system temperature,
- the precipitable water vapor,
- and the zenithal opacity.

Their exact values are evaluated for the frequency at the middle of the chunk4.1. The values at other frequencies in the chunk can be evaluated using one of the two available modes:

1. in the flat mode, the central values are reused over all the chunk bandwidth.
2. the second mode is interpolation. In this case, the chunks are reordered by ascending frequency, and the values at non-central frequencies are interpolated between the current chunk and its nearest neighbour, so that it is computed at the frequency of the desired channel. This has the advantage to avoid discontinuities along the whole bandwidth and thus to avoid calibration platforming. For the two half-chunks at the boundary of the whole bandwidth, where no neighbour chunk is available, the values are extrapolated from the boundary chunk and its neighbour on the other side.