This data set contains cloud base heights derived from the Multi-angle Imaging SpectroRadiometer (MISR) which is placed on the Terra satellite. The cloud base heights are provided globally on a 0.25x0.25 degree longitude latitude grid for a three year period (2007-2009). Daily files comprise retrievals from the illuminated portion of about 14 Terra revolutions around the Earth.
The newly developed MISR cloud base height (MIBase) algorithm (Boehm et al., in review 2018, DOI:10.5194/amt-2018-317) retrieves the cloud base height from the MISR Level 2TC Cloud Product (MIL2TCSP). The MIL2TCSP product provides the cloud top height and a stereo-derived cloud mask at 1.1 km horizontal resolution. The MIBase algorithm evaluates the ensemble of the cloud top height retrievals for each grid box in case some cloud gaps occur within the area and a sufficient amount of cloud top height retrievals marked high confidence cloud according to the stereo-derived cloud mask is provided. The 15th percentile of the cloud top height distribution within the respective grid box yields the cloud base height. The algorithm has been calibrated and validated against ground-based ceilometer measurements across the continental USA over the course of two years.
An important strength of MIBase is the geometric approach which is applied to create the cloud top height product from MISR measurements. Neither a calibration nor auxiliary data are necessary to obtain the cloud top height product which is the starting point for the MIBase algorithm. In consequence, retrievals are possible over all kinds of terrain even above ice. A disadvantage is the threshold height which MISR requires to create the stereo-derived cloud mask. Therefore, depending on the terrain variability in the vicinity of the measurement, MIBase is not capable of deriving cloud base heights below at least 560 m (flat terrain). The algorithm requires a broken cloud scene. For complete overcast within the chosen MIBase cell, the cloud base height cannot be retrieved. Therefore, climatologies derived from this algorithm would be biased towards cloud types for which MISR is able to observe the surface through cloud gaps. The given cloud base height estimates represent the situation during morning hours since MISR is carried on board the Terra satellite in a Sun-synchronous orbit with an equatorial overpass time at around 10:30 local solar time.
Data gaps (due to unavailable input data):
2008-10-01 - 2008-10-15 and
2008-12-20 - 2008-12-22
