Observation Model

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Reijo Keskitalo


This is not a logbook entry but rather a portal page for CMB-S4 Observation Model. It collects information about the scanning strategy options and constraints.


CMB-S4 requires four distinct scan strategies to cover two telescope types at two different sites.

Chile LAT (Legacy Survey)

Chile LAT strategy is designed to optimize the effective sky area and cadence. The most advanced proposal is the modulated high cadence strategy, capable of delivering a uniform depth survey over ~70% of the sky and a daily cadence. The downside is that the strategy requires accelerating the telescope scan rate towards the turnarounds.

Pole LAT (Delensing Survey)

Pole LAT survey is optimized to support the Pole SAT survey. Since the footprint of the LAT differs from the SAT in shape and size, following the same boresight would leave much of the SAT patch unobserved.

Open question: How should the SAT apodization region be covered? Uniform LAT coverage or similar apodization profile? It is complicated to produce an observing schedule for that LAT that would produce a matching depth map for the two telescopes.

Pole SAT

The South Pole SATs will scan in either deep or wide mode. The depth of the deep scan is limited by the throw width required to disentangle scan-synchronous systematics from the sky signal. The optional wide survey is limited by the amount of low foreground sky visible from the South Pole.

Chile SAT

Observing a deep field from Chile is difficult due to the sky rotation. The current proposal for Chile SAT strategy calls for designating two, deep fields that are embedded in a wedding cake fashion in secondary and tertiary fields that wrap around the sky in Right Ascension to optimize the scanning efficiency. The deep fields are always targeted when available and the remaining integration time is directed towards the lower tiers.