Alexander P. Trishchenko

Removal of systematic seasonal atmospheric signal from interferometric synthetic aperture radar ground deformation time series

Applying the Multidimensional Small Baseline Subset interferometric synthetic aperture radar algorithm to about 1500 Envisat and RADARSAT-2 interferograms spanning 2003-2013, we computed time series of ground deformation over Naples Bay Area in Italy. Two active volcanoes, Vesuvius and Campi Flegrei, are located in this area in close proximity to the densely populated city of Naples. For the first time, and with remarkable clarity, we observed decade-long elevation-dependent seasonal oscillations of the vertical displacement component with a peak-to-peak amplitude of up to 3.0 cm, substantially larger than the long-term deformation rate (<0.6 cm/yr). Analysis, utilizing surface weather and radiosonde data, linked observed oscillations with seasonal fluctuations of water vapor, air pressure, and temperature in the lower troposphere. The modeled correction is in a good agreement with observed results. The mean, absolute, and RMS differences are 0.014 cm, 0.073 cm, and 0.087 cm, respectively. Atmospherically corrected time series confirmed continuing subsidence at Vesuvius previously observed by geodetic techniques.

Mapping of Surface Albedo over Mackenzie River Basin from Satellite Observations

This chapter presents the approach and results of mapping surface albedo and bi-directional reflectance distribution function (BRDF) properties over the Mackenzie River Basin (MRB). Satellite observations from three types of sensors were used: (1) the Advanced Very High Resolution Radiometer (AVHRR) sensor onboard the NOAA platforms, (2) the VEGETATION (VGT) sensor onboard the SPOT platforms, and (3) the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard the TERRA platform. The data collected using these sensors span the period of 1985 to 2004. Seasonal and interannual variability of spectral and broadband albedo over the MRB was analyzed. Broadband albedo averaged over the region changed from 0.11±0.03 in summer to 0.4-0.55 in winter. No substantial long-term systematic trends in surface albedo could be detected over the study period, mainly due to large interannual variability, uncertainties in sensors properties, atmospheric correction, and retrieval procedure.

Concept of a new multiangular satellite mission for improved bidirectional sampling of surface and atmosphere properties

While existing satellite Earth Observing (EO) systems provide many baseline observations, they are lacking an important combination of capabilities in terms of angular sampling, spectral coverage, and spatial resolution. This has an impact on the accuracy of retrievals and the capability to provide accurate regular operational monitoring of surface and atmospheric properties on a large scale (global or continental). The concept of Advanced Multiangular MEdium Resolution System (AMMERS), that addresses the above issues and provides unique capability presently unavailable from other space observing systems, is proposed here. The missions unique feature is a combination of medium resolution (400m), multi-spectral observations (13 spectral bands in visible, NIR, SWIR, IR, SW and LW), and multi-angular capabilities (7 angles). AMMERSs multiangular features and swath width allow bi-directional angular sampling close to the solar principal plane and in the perpendicular plane. These capabilities are critically important for accurate estimation of surface albedo, vegetation structure, and forest parameters. AMMERS will also be superior to many other missions in retrieving SST, aerosol, clouds parameters, snow, and wild fire mapping.

Retrieval of BRDF for pure landcover types from MODIS and MISR using an angular unmixing approach

Information about the surface bi-directional reflectance distribution function (BRDF) and albedo is required as a boundary condition for radiative transfer modeling, aerosol retrievals, cloud retrievals, and atmospheric modeling. The typical spatial resolution provided by MODIS and MISR standard surface products (~1km) is insufficient to measure the BRDF of the pure surface types, because most pixels at this scale correspond to mixed classes. We present an approach for the retrieval of the basic surface BRDFs from the observations of MODIS/Terra and MISR using an angular unmixing method. Our analysis is focused on the Atmospheric Radiation Measurement (ARM) Program area in the Southern Great Planes (SGP) region, which is a predominantly agricultural area with a few major crop types. Pure surface classes were identified using high-resolution (30m) Landsat imagery and results of a ground survey. Assuming that the reflectance for each coarse pixel is a linear superposition of reflectances of basic surface types, it is possible to estimate the original BRDF parameters for each landcover type. In our case, three dominant classes were selected: wheat, grass, and baresoil. In the case of wheat and grass, the dispersion of the results is smaller than in the case of soil. This can be explained by the relatively low fractional coverage of the soil class within large pixels and by the significant variability of soil reflectance depending on wetness, soil type (sand, clay, etc.), and other factors. The correlation between the BRDF shape factors and the normalized difference vegetation index (NDVI) has also been analyzed. There is a high degree of correlation between the NDVI and BRDF isotropic factor (r0 in the case of MISR), while the correlation with other BRDF parameters was found to be smaller. In general, the NDVI can be used as a crude proxy for the BRDF shape.

BRDF/Albedo retrievals from the Terra and Aqua MODIS systems at 500-m spatial resolution and 10-day intervals

Surface bi-directional reflectance distribution function (BRDF) and albedo properties are retrieved over the Atmospheric Radiation Measurement (ARM) Program Southern Great Plains (SGP) area. A landcover-based fitting approach is employed by using a newly developed landcover classification map and the MODIS 10-day surface reflectance product (MOD09). The surface albedo derived by this method is validated against other satellite systems (e.g. Landsat-7 and MISR) and ground measurements made by an ASD spectroradiometer. Our results show good agreements between the datasets in general. The advantages of this method include the ability to capture rapid changes in surface properties and an improved performance over other methods under a frequent presence of clouds. Results indicate that the developed landcover-based fitting methodology is valuable for generating spatially and temporally complete surface albedo and BRDF maps using MODIS observations.

Wildfire Aerosol and Cloud Radiative Forcing in the Mackenzie River Basin from Satellite Observations

Clouds and wildfire aerosols are both important in our understanding of the radiation budgets in the Mackenzie River Basin (MRB). The smoke aerosols produced by wildfires are predominately aerosols that can absorb incoming solar radiation in the atmosphere. Both the cloud and wildfire aerosol radiative forcing at the top of atmosphere (TOA) and at the surface in the MRB are investigated. Second-order polynomial relationships are found between forcing ( Δ F) and aerosol optical thickness (τ) for the reflected solar fluxes at the TOA, the outgoing longwave (LW) fluxes at the TOA, and the net surface solar fluxes. The monthlymean basin-average cloud shortwave forcing at the TOA and at the surface between June and September are between 150 and 200Wm-2 and -160 and -220 W M-2, respectively, while the basin-averaged outgoing LW cloud forcing at the TOA is around -40 W m-2. Overall, the cloud forcing could impact the shortwave and longwave radiation budgets by 30–50% both at the TOA and at the surface for the MRB region.