Disclaimer: This material is being kept online for historical purposes. Though accurate at the time of publication, it is no longer being updated. The page may contain broken links or outdated information, and parts may not function in current web browsers. Visit https://espo.nasa.gov for information about our current projects.

 

Fusion of MISR Stereo Cloud Heights and Terra-MODIS Thermal Infrared Radiances...

Mitra, A., J. Loveridge, and L. Di Girolamo (2023), Fusion of MISR Stereo Cloud Heights and Terra-MODIS Thermal Infrared Radiances to Estimate Two-Layered Cloud Properties, J. Geophys. Res..
Abstract: 

Our longest, stable record of cloud-top pressure (CTP) and cloud-top height (CTH) are derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-Angle Imaging Spectroradiometer (MISR) on Terra. Because of single cloud-layer assumptions in their standard algorithms, they provide only single CTP/CTH retrievals in multi-layered situations. In the predominant multi-layered regime of thin cirrus over low clouds, MODIS significantly overestimates cirrus CTP and emissivity, while MISR accurately retrieves low-cloud CTH. Utilizing these complementary capabilities, we develop a retrieval algorithm for accurately determining both-layer CTP and cirrus emissivity for such 2-layered clouds, by applying the MISR low-cloud CTH as a boundary condition to a modified MODIS CO2-slicing retrieval. We evaluate our 2-layered retrievals against collocated Cloud-Aerosol Transport System (CATS) lidar observations. Relative to CATS, the mean bias of the upper cloud CTP and emissivity are reduced by ∼90% and ∼75% respectively in the new technique, compared to standard MODIS products. We develop an error model for the 2-layered retrieval accounting for systematic and random errors. We find up to 87% of all residuals lie within modeled 95% confidence intervals, indicating a near-closure of error budget. This reduction in error leads to a reduction in modeled atmospheric longwave radiative flux biases ranging between 5 and 40 W m −2, depending on the position and optical properties of the layers. Given this large radiative impact, we recommend that the pixel-level 2-layered MODIS + MISR fusion algorithm be applied over the entire MISR swath for the 22-year Terra record, leading to a first-of-its-kind 2-layered cloud climatology from Terra's morning orbit. Plain Language Summary Our longest climate-quality record of global cloud-top heights (CTH) comes from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-Angle Imaging Spectroradiometer (MISR) on the Terra satellite. These sensors assume a single cloud-layer in retrieving CTH, even though ∼30% of global cloud cover is multi-layered. Multi-layered clouds predominantly consist of thin ice clouds over low clouds. Under such conditions, MISR accurately retrieves low-cloud CTH, while MODIS systematically underestimates upper-cloud-layer CTH. Here, we have developed a 2-layered MODIS + MISR fusion CTH retrieval by using MISR's accurate low-cloud CTH as an input to a modified MODIS algorithm. This algorithm combines the complementary capabilities of MISR and MODIS in distinguishing higher and lower clouds and estimates both-layer cloud heights and high-cloud emissivity. Through comparisons against coincident Cloud-Aerosol Transport System lidar observations, we find that the new algorithm improves the accuracies in retrieved CTH and cloud emissivities by ∼75% over standard MODIS products. We further demonstrate significant improvements in estimates of simulated atmospheric longwave radiation from our implementation. Owing to its large radiative impact, we suggest that the pixel-level fusion algorithm be applied to all 22 years of Terra record to facilitate public dissemination of the first 2-layered cloud record from its morning orbit.

Research Program: 
Radiation Science Program (RSP)
Mission: 
Terra-MISR
Terra-MODIS
ISS-CATS
Funding Sources: 
MISR project contract 147871 with the Jet Propulsion Laboratory, California Institute of Technology. Partial support from the NASA ACCESS program under contract NNX16AMO7A is also acknowledged.