Comments on Use Case: FRAM or LIDAR down
Summary
In general, I would distinguish this Use Case between:
- FRAM or LIDAR down
- FRAM and LIDAR down
Case 1. can be divided into the two sub-cases:
1.1 FRAM or LIDAR (whatever is operating) observe stable conditions, i.e. no clouds, a stable ground-layer height and AOD.
1.2 FRAM or LIDAR (whatever is operating) observe unstable conditions.
In the first case, an almost standard analysis can be made, with the aerosol transmission hypercubes calculated assuming a slow component only. The CTC can be used to re-check whether a fast component has escaped the LIDAR or FRAM observations and possibly treat such a part of the data set differently (e.g. by excluding it).
In the case of FRAM only data, a lack of fast component normally points towards a scenario of no clouds, hence a typical aerosol ground layer height, according to AOD and obtained from the analysis of historical data, can be assumed, with an increased systematic uncertainty. In the case of Raman LIDAR only, aerosol extinction profiles can be interpolated in time. Since no FRAM data is available, the LIDAR profiles need to be assumed to be representative for the observed field-of-view.
In the second case, the CTC shall be used to identify those parts of the OB affected by fast variations. According to the science case, these data can either get excluded or get attached a larger systematic uncertainty. In the latter case and Raman LIDAR only, aerosol extinction profiles can be used to identify the height of clouds (or a changing ground layer) and the CTC to identify which periods of time are affected by the cloud (or ground layer change). In the case of FRAM only, a typical cloud height (found by analysis of historical LIDAR data) needs to be assumed, with an appropriate systematic uncertainty that reflects the missing knowledge of the actual cloud height.
Case 2. can be divided into the two sub-cases:
2.1 CTC observes stable conditions and values typical for a clear night.
2.2 CTC observes unstable conditions.
In the first case, an almost standard analysis can be made, assuming a typical clear-night case and an increased systematic uncertainty.
In the second case, the data set shall be excluded, or only if absolutely necessary, analysed assuming typical cloud heights varying in time according to the CTC. In the last case, a maximum lack of knowledge about the cloud altitude needs to be assumed and the systematic uncertainty scaled accordingly.