Catherine Moroney

Operational retrieval of cloud-top heights using MISR data

Due to its unique nine-angle configuration, the Multi-angle Imaging SpectroRadiometer (MISR) can retrieve cloud parameters such as cloud-motion vectors and cloud-top heights using a purely geometrical technique that involves locating the same cloud features at different viewing angles. The geometrical nature of this technique means that the retrievals are relatively insensitive to the absolute instrument calibration. Fast stereo-matching algorithms have been developed to perform this image matching automatically on an operational basis. Preliminary results are shown of the operational retrievals together with comparisons against other data. Cloud-top height is generally obtained on a 1.1-km grid with an accuracy of /spl plusmn/ 562 m, even over snow and ice. The limitations of the technique, resulting at times in height blunders, noisy retrievals, and discrete effects of wind correction, are discussed.

Aerosol source plume physical characteristics from space‐based multiangle imaging

Models that assess aerosol effects on regional air quality and global climate parameterize aerosol sources in terms of amount, type, and injection height. The multiangle imaging spectroradiometer (MISR) aboard NASAs Terra satellite retrieves total column aerosol optical thickness (AOT), and aerosol type over cloud-free land and water. A stereo-matching algorithm automatically retrieves reflecting-layer altitude wherever clouds or aerosol plumes have discernable spatial contrast, with about 500-m accuracy, at 1.1-km horizontal resolution. Near-source biomass burning smoke, volcanic effluent, and desert dust plumes are observed routinely, providing information about aerosol amount, particle type, and injection height useful for modeling applications. Compared to background aerosols, the plumes sampled have higher AOT, contain particles having expected differences in Angstrom exponent, size, single-scattering albedo, and for volcanic plume and dust cloud cases, particle shape. As basic thermodynamics predicts, thin aerosol plumes lifted only by regional winds or less intense heat sources are confined to the boundary layer. However, when sources have sufficient buoyancy, the representative plumes studied tend to concentrate within discrete, high-elevation layers of local stability; the aerosol is not uniformly distributed up to a peak altitude, as is sometimes assumed in modeling. MISR-derived plume heights, along with meteorological profile data from other sources, make it possible to relate radiant energy flux observed by the moderate resolution imaging spectroradiometer (MODIS), also aboard the Terra spacecraft, to convective heat flux that plays a major role in buoyant plume dynamics. A MISR climatology of plume behavior based on these results is being developed.

MISR Stereo Heights of Grassland Fire Smoke Plumes in Australia

Plume heights from wildfires are used in climate modeling to predict and understand trends in aerosol transport. This paper examines whether smoke from grassland fires in the desert regions of western and central Australia ever rises above the atmospheric boundary layer. Three methods for deriving plume heights from the Multi-angle Imaging SpectroRadiometer (MISR) instrument were utilized: (1) the MISR standard stereo-height algorithm; (2) the MISR enhanced stereo product; and (3) the MISR INteractive eXplorer (MINX) v.1 tool. To provide context and to search for correlative factors, stereo heights were combined with fire radiant energy flux from the Moderate Resolution Imaging Spectroradiometer instrument, atmospheric structure information from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis project model, surface cover from the Australia National Vegetation Information System, and forward and backward trajectories from the National Oceanic and Atmospheric Administration Hybrid Single-Particle Lagrangian Integrated Trajectory model. Although most smoke plumes concentrate in the near-surface boundary layer as expected, some appear to rise higher. Smoke that gets above the boundary layer will travel farther, remain in the atmosphere longer, and therefore have a larger environmental impact. It was previously thought unlikely for grassland fires to inject smoke above the boundary layer. Our findings suggest that climate modelers should reevaluate common assumptions about the heights of smoke plumes when producing aerosol transport models involving grassland fires. A closer examination of grassland fire energetics may also be warranted.

On the angular radiance closure of tropical cumulus congestus clouds observed by the Multiangle Imaging Spectroradiometer

over a (2.2 km) 2 area, and (5) a vertical-mean b retrieved using off-nadir reflectances. An asymmetry about nadir in the observed reflectance means and skewnesses is not reproduced by any Monte Carlo simulation. The lack of symmetry can be related to differing proportions of unobscured sunlit and shadowed cloudy areas within the different views, even for these cases with viewing angles close to the perpendicular plane. The Monte Carlo simulations do not appear to capture the observed fraction of unobscured sunlit and shadowed cloudy areas, suggesting that radiatively significant cloud variability is occurring at scales smaller than the height field resolution of ±550 m. Results from the Monte Carlo simulation done at a higher vertical resolution are consistent with this. The cases examined also contain a nadir maximum in the observed reflectance skewnesses and a relative maximum for the observed nadir reflectances, attributed to the solar illumination of some optically thick cloud surfaces and to specular reflection pervading through the optically thin cloudy regions. This contrasts with previous modeling results that assume a Lambertian surface. INDEX TERMS: 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3374 Meteorology and Atmospheric Dynamics: Tropical meteorology; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; KEYWORDS: 3-D radiative transfer, cumulus congestus, MISR

Use of stereo-matching to coregister multiangle data from MISR

The pattern-matching algorithms originally developed for Multi-angle Imaging SpectroRadiometer (MISR) (flying on the Earth Observing System (EOS) Terra platform) cloud retrieval have also proven useful in independently providing quality assurance of the coregistration of multiangle measurements with the nadir view. Two new techniques developed to test the coregistration are described in this paper along with results of the misregistration detection on both historical and current data. No ground-control points are strictly necessary for these calculations-just simultaneous clear-sky land imagery for three cameras and knowledge of the terrain altitude. The difficulty of registration increases with the obliquity of the view angle, so our emphasis is on coregistering to the nadir view. This paper also provides proxy validation of the stereo-matching algorithms for clear-sky land scenes.

Multiangle Observations of Arctic Clouds from FIRE ACE: June 3, 1998 Case Study

In May and June 1998 the Airborne Multiangle Imaging Spectroradiometer (AirMISR) participated in the FIRE Arctic Cloud Experiment (ACE). AirMISR is an airborne instrument for obtaining multiangle imagery similar to that of the satellite-borne MISR instrument. This paper presents a detailed analysis of the data collected on June 3, 1998. In particular, AirMISR radiance measurements are compared with measurements made by two other instruments, the Cloud Absorption Radiometer (CAR) and the MODIS airborne simulator (MAS), as well as to plane-parallel radiative transfer simulations. It is found that the AirMISR radiance measurements and albedo estimates compare favorably both with the other instruments and with the radiative transfer simulations. In addition to radiance and albedo, the multiangle AirMISR data can be used to obtain estimates of cloud top height using stereoimaging techniques. Comparison of AirMISR retrieved cloud top height (using the complete MISR-based stereoimaging approach) shows excellent agreement with the measurements from the airborne Cloud Lidar System (CLS) and ground-based millimeter-wave cloud radar.

Assessment of MISR Cloud Motion Vectors (CMVs) Relative to GOES and MODIS Atmospheric Motion Vectors (AMVs)

AbstractCloud motion vector (CMV) winds retrieved from the Multiangle Imaging SpectroRadiometer (MISR) instrument on the polar-orbiting Terra satellite from 2003 to 2008 are compared with collocated atmospheric motion vectors (AMVs) retrieved from Geostationary Operational Environmental Satellite (GOES) imagery over the tropics and midlatitudes and from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery near the poles. MISR imagery from multiple view angles is exploited to jointly retrieve stereoscopic cloud heights and motions, showing advantages over the AMV heights assigned by radiometric means, particularly at low heights (<3 km) that account for over 95% of MISR CMV sampling. MISR–GOES wind differences exhibit a standard deviation ranging with increasing height from 3.3 to 4.5 m s−1 for a high-quality [quality indicator (QI) ≥ 80] subset where height differences are <1.5 km. Much of the observed difference can be attributed to the less accurately retrieved component of CMV motion along the...

Cloud heights measured by MISR from 2000 to 2015

Davies and Molloy (2012) reported a decrease in the global effective cloud height over the first 10 years of Multiangle Imaging Spectroradiometer (MISR) measurements on the Terra satellite. We have reexamined their time series for possible artefacts that might especially affect the initial portion of the record when the heights appeared anomalously high. While variations in sampling were shown to be inconsequential, an artefact due to the change in equator crossing time that affected the first 2 years was discovered, and this has now been corrected. That correction, together with the extension of the time series by five more years, yields no significant overall trend in global heights during the first 15 years of Terra operation. The time series is dominated by large interannual fluctuations associated with La Nina events that mask any overall trend on a global scale. On a regional basis, the cloud heights showed significant interannual variations of much larger amplitude, sometimes with fairly direct cancellation between regions. There were unexplained differences between the two hemispheres in the timing of height anomalies. These differences persisted over a large range of extratropical latitudes, suggestive of teleconnections. Within the tropics, there were very strong changes associated with the Central Pacific and Indonesian Maritime Continent regions that oscillated out of phase with each other, with interannual amplitudes that exceeded 1 km.

Future Mission Concept for Operational Retrieval of Cloud-Top Heights and Cloud Motion Wind Vectors

To meet operational demands for vertically-resolved atmospheric winds, we propose a wide-swath multiangle stereo imaging system that could be easily integrated into future satellite platforms. The concept uses techniques proven with the multi-angle imaging spectroradiometer (MISR) instrument, currently flying in polar low-Earth orbit (LEO) on NASAs Terra satellite. MISR has demonstrated the feasibility of obtaining accurate stereophotogrammetric retrievals of cloud and aerosol plume heights and height-resolved cloud-tracked wind vectors. MISR obtains multiangle imagery with along-track pointing angles ranging from nadir to 70deg forward and backward of nadir and makes use of the several-minute time delay among a triplet of multiangle views to separate the effects of wind displacement from height-induced stereoscopic parallax. Careful attention to multiangle image co-registration (crucial for obtaining accurate wind retrievals) has led to wind estimates that exhibit negligible bias relative to reanalysis data. The root-mean-square uncertainty in speed is estimated to be in the 1-3 m/sec range, depending on whether the wind component is parallel or perpendicular to the flight direction and on the degree of quality control applied. The uncertainty in height assignment is on the order of 300 mum. Comparison of results from a forward-viewing angle triplet with independent retrievals from a backward-viewing triplet provides an important control on retrieval quality. A key attribute of the stereophotogrammetric approach to retrieving cloud heights (and winds) is that the technique is purely geometric. Accurate radiometric calibration is not required, thereby enabling significant simplification of a future instrument dedicated to stereo height and wind retrievals. Furthermore, the approach is insensitive to atmospheric temperature profiles and cloud emissivities, and provides data of consistent quality at all latitudes from polar orbit. It is also purely passive, so sensor lifetime is not a major issue. Since the technique relies on pattern matching, only a single mid-visible spectral band is required (a separate thermal infrared band, e.g., at 3.7 mum, would be needed in order to acquire measurements at night). Future improvements in computer capability will enable improved pattern-matching algorithms that could be implemented operationally. This simple, compact, and relatively inexpensive concept would assist numerical weather prediction models by retrieving cloud-motion vector winds in traditionally data-sparse areas (mid-oceans and high latitudes), would continue the unique data record begun with MISR by establishing long-term cloud-top height and cloud-motion wind monitoring with sensitivities capable of detecting atmospheric response to climate forcings, and would provide global measurements of the injection and transport heights of distinct aerosol plumes from wildfires, dust storms, and volcanic eruptions.