## 2 Clouds Properties from Infrared and Microwave Satellite Observations
### Infrared Observations Only
A study of MODIS CLWP uncertainties at high latitudes for mixed-phase clouds is presented by [78] with many instruments (i.e., AMSR-E, CloudSat, and CALIPSO). The results of multisensor CLWP retrievals show a CIWP-related CLWP bias, reaching almost 15% with CIWP of 150 g/m\({}^{2}\) and 40% or higher when CIWP is greater than 400 g/m\({}^{2}\), in the case of mixed-phase clouds like liquid clouds. Furthermore, the unresolved angle-dependent bias of the solar zenith in MODIS CLWP, mainly caused by the variation in the cloud-top height due to three-dimensional radiative interactions with cloud-top inhomogeneity, is studied. It is possible to reduce the bias by 25 g/m\({}^{2}\) with a solar zenith angle of 80\({}^{\circ}\) and improve the agreement with AMSR-E CLWP trends by excluding only 0.5% of the data points that show significant errors. It is possible to retrieve optical cloud properties and cloud height properties at the pixel level using the MODIS Level-2 cloud product (MOD06/MYD06 for Terra and Aqua MODIS, respectively); see [79]. Further information can be obtained with several product updates introduced in Collection 6. However, since the computations are considered to yield baseline uncertainty due to sources of errors to the linear assumption inherent in the calculations, uncertainties on the order of 50% are expected to be of little value for science works. However, in single-layer cloud situations, ref. [80] find that the MODIS cloud algorithm produces cloud-top pressures within 50 hPa of lidar determinations. In the case of optically thick clouds, ref. [81] demonstrated that ice cloud retrieval uncertainties in diurnal variation can be reduced by considering infrared measurements, temperature dependence, and ice particle habits. The properties of ice-over-water were characterized by using the algorithm developed by [82]. The algorithm, which uses only the solar channels available on the MODIS and the Visible Infrared Imaging Radiometer Suite (VIIRS) sensors, is available for the case of an ice-over-water cloud with ice COT smaller than 7 and for an optically thicker liquid-water cloud (water COT > 5). The methodologies for retrieving the effective diameter size and cloud optical thickness analyzed so far do not yield positive results for convective clouds with 3D morphology. Ref. [83] dedicate a study to this problem using MODIS, which includes channels in the shortwave IR with a single viewing angle, and the Multi-angle Imaging SpectroRadiometer (MISR), which provides multi-angle imagery in the visible and near-IR, MODIS. The combined use of both in the future should enable 3D retrievals of the effective size of cloud particles and extinction fields. A similar study was conducted by [84], regarding the retrieval of cloud-top pressure and cloud-top height in the predominant multilayer regime of thin cirrus clouds above low clouds. They attempted to remedy the significant overestimation of the CTP and of cirrus emissivity via MODIS using the accuracy of low clouds' CTH retrieval through MISR. With this methodology, validated against Cloud-Aerosol Transport System (CATS) lidar observations, the average upper cloud CTP bias and emissivity are reduced by 90% and 75%, respectively, compared to standard MODIS products. The MISR-MODIS synergy was also exploited by [85]. Using a full year of data (2013) and a variable ice particle roughness model, the authors investigated the retrieved ice cloud optical thickness, \(\mathrm{D_{e}}\), and CIWP over oceans under different conditions. In evaluating the annual cycles, this methodology provides a better understanding of the operational MODIS Collection 6 retrieved products. Based on the Aqua MODIS and VIIRS SNPP products, the CLouD PROperties (CLD-PROP) product algorithms follow a \"continuity of approach\" paradigm for recording cloud properties. Given the strong scientific implications, ref. [79] illustrates details and impacts.