Abstract
Cloud-top heights (CTH) from the Multiangle Imaging Spectroradiometer
(MISR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) on
Terra constitute our longest-running single-platform CTH record from a
stable orbit. Here, we provide the first evaluation of the Terra Level 2
CTH record against collocated International Space Station Cloud-Aerosol
Transport System (CATS) lidar observations between 50ºN - 50ºS. Bias and
precision of Terra CTH relative to CATS, calculated from the normality
of CTH error histograms, are shown to be strongly tied to cloud
horizontal and vertical heterogeneity and altitude. For single-layered,
unbroken, optically thick clouds observed for all altitudes, the
uncertainty in MODIS and MISR CTH are -540±690 m and -280±370 m,
respectively. The uncertainties are generally smaller for lower altitude
clouds and larger for optically thinner clouds. For multi-layered
clouds, errors are summarized herein using both absolute CTH and
CATS-layer-altitude proximity to Terra CTH. We show that MISR detects
the lower cloud in a two-layered system, provided top-layer optical
depth < ~0.3, but MISR low-cloud errors are
unaltered by the presence of thin cirrus. Systematic and random errors
are propagated to explain inter-sensor disagreements, as well as to
provide the first estimate of MISR stereo-opacity bias. For MISR,
altitude-dependent wind-retrieval bias (-90 to -110 m) and
stereo-opacity bias (-110 to -240 m) and for MODIS, bias due to low
opacity near cloud-top lead to overall negative CTH bias. MISR’s
precision is largely driven by wind-speed uncertainty (3.7 m s-1),
whereas MODIS precision is driven by forward-modeling uncertainty.