Valeriy Kovalskyy

The Suitability of Multi-temporal Web-enabled Landsat Data NDVI for Phenological Monitoring – a Comparison with Flux Tower and MODIS NDVI

Three years of flux-tower-derived normalized difference vegetation index (NDVI) data were compared with contemporaneous 30 m web-enabled Landsat data (WELD) and with 500 m Moderate-Resolution Imaging Spectroradiometer (MODIS) nadir bidirectional reflectance distribution function-adjusted reflectance (NBAR) NDVI data to assess the relative suitability of these different resolutions of freely available satellite data for phenological monitoring. Comparisons were made at two flux tower sites in the United States with average to above average cloud cover. The WELD 30 m NDVI data were found to have higher correlation with the flux tower NDVI data than the MODIS 500 m NBAR NDVI data. The dates of vegetation green-up onset and maximum-greenness onset, derived using an established phenological metric extraction methodology, were generally closer between the flux tower and WELD NDVI data than between the flux tower and MODIS NBAR data. These results indicate that the WELD NDVI time series is suitable for 30 m scale phenological monitoring.

Evapotranspiration variability and its association with vegetation dynamics in the Nile Basin, 2002–2011

Abstract: Evapotranspiration (ET) is a vital component in land-atmosphere interactions. In drylands, over 90% of annual rainfall evaporates. The Nile Basin in Africa is about 42% dryland in a region experiencing rapid population growth and development. The relationship of ET with climate, vegetation and land cover in the basin during 2002–2011 is analyzed using thermal-based Simplified Surface Energy Balance Operational (SSEBop) ET, Normalized Difference Vegetation Index (NDVI)-based MODIS Terrestrial (MOD16) ET, MODIS-derived NDVI as a proxy for vegetation productivity and rainfall from Tropical Rainfall Measuring Mission (TRMM). Interannual variability and trends are analyzed using established statistical methods. Analysis based on thermal-based ET revealed that >50% of the study area exhibited negative ET anomalies for 7 years (2009, driest), while >60% exhibited positive ET anomalies for 3 years (2007, wettest). NDVI-based monthly ET correlated strongly (r > 0.77) with vegetation than thermal-based ET (0.52 < r < 0.73) at

A One Year Landsat 8 Conterminous United States Study of Cirrus and Non-Cirrus Clouds

The first year of available Landsat 8 data over the conterminous United States (CONUS), composed of 11,296 acquisitions sensed over more than 11 thousand million 30 m pixel locations, was analyzed comparing the spatial and temporal incidence of 30 m cloud and cirrus states available in the standard Landsat 8 Level 1 product suite. This comprehensive data analysis revealed that on average over a year of CONUS observations (i) 35.9% were detected with high confidence cloud, with spatio-temporal patterns similar to those observed by previous Landsat 5 and 7 cloud analyses; (ii) 28.2% were high confidence cirrus; (iii) 20.1% were both high confidence cloud and high confidence cirrus; and (iv) 6.9% were detected as high confidence cirrus but low confidence cloud. The results illustrate the potential of the 30 m cloud and cirrus states available in the standard Landsat 8 Level 1 product suite but imply that the historical CONUS Landsat archive has about 7% of undetected cirrus contaminated pixels. Systematic cloud detection commission errors over a minority of highly reflective exposed soil/sand surfaces were found and it is recommended that caution be taken when using the currently available Landsat 8 cloud data over similar surfaces.

Optimal Solar Geometry Definition for Global Long-Term Landsat Time-Series Bidirectional Reflectance Normalization

The systematic generation of global Landsat time-series products has been advocated, and studies have suggested the need to minimize Landsat reflectance anisotropy effects. Considering a global year of non-Antarctic Landsat 5 and 7 acquisitions, the scene center solar zenith varied from 22.14° to 89.71°, with a mean of 43.23°. However, a solar zenith angle definition suitable for generation of global bidirectional reflectance normalized Landsat time series has not been considered. In this paper, a solar zenith optimal definition is developed in terms of the following criteria: i) ensuring that it can be modeled for any location and date; ii) ensuring that it is constant or smoothly changing with respect to space and time and has global annual variation no greater than the variation in the observed Landsat solar zenith angles

Change and persistence in land surface phenologies of the Don and Dnieper river basins

(\theta_{s})

The Utility of Landsat Data for Global Long Term Terrestrial Monitoring

; and iii) minimizing the differences between

Exploring the middle infrared region for urban remote sensing: seasonal and view angle effects

\theta_{s}

Evaluation of rule-based classifier for Landsat-based automated land cover mapping in South Africa

and the solar zenith angle used for normalization. Global coverage Landsat data are used to evaluate four solar zenith angle definitions, namely, fixed solar zenith angles, i.e.,

Viewing Global Megacities Through MODIS

(\theta_{\mathrm{fixed}})

4\hbox{-}\upmu \text{m}

, the solar zenith at local solar noon, i.e.,