Showing papers by "John M. Kovacs published in 2020"
TL;DR: The Sentinel-1 constellation provides a great data source for detecting crop field management activities through coherent or incoherent change detection techniques, given its mechanism to acquire images with InSAR capability at 12-day revisiting cycle with a single satellite for most part of the Earth.
Abstract: Synthetic aperture radar (SAR) is more sensitive to the dielectric properties and structure of the targets and less affected by weather conditions than optical sensors, making it more capable of detecting changes induced by management practices in agricultural fields. In this study, the capability of C-band SAR data for detecting crop seeding and harvest events was explored. The study was conducted for the 2019 growing season in Temiskaming Shores, an agricultural area in Northern Ontario, Canada. Time-series SAR data acquired by Sentinel-1 constellation with the interferometric wide (IW) mode with dual polarizations in VV (vertical transmit and vertical receive) and VH (vertical transmit and horizontal receive) were obtained. interferometric SAR (InSAR) processing was conducted to derive coherence between each pair of SAR images acquired consecutively in time throughout the year. Crop seeding and harvest dates were determined by analyzing the time-series InSAR coherence and SAR backscattering. Variation of SAR backscattering coefficients, particularly the VH polarization, revealed seasonal crop growth patterns. The change in InSAR coherence can be linked to change of surface structure induced by seeding or harvest operations. Using a set of physically based rules, a simple algorithm was developed to determine crop seeding and harvest dates, with an accuracy of 85% (n = 67) for seeding-date identification and 56% (n = 77) for harvest-date identification. The extra challenge in harvest detection could be attributed to the impacts of weather conditions, such as rain and its effects on soil moisture and crop dielectric properties during the harvest season. Other factors such as post-harvest residue removal and field ploughing could also complicate the identification of harvest event. Overall, given its mechanism to acquire images with InSAR capability at 12-day revisiting cycle with a single satellite for most part of the Earth, the Sentinel-1 constellation provides a great data source for detecting crop field management activities through coherent or incoherent change detection techniques. It is anticipated that this method could perform even better at a shorter six-day revisiting cycle with both satellites for Sentinel-1. With the successful launch (2019) of the Canadian RADARSAT Constellation Mission (RCM) with its tri-satellite system and four polarizations, we are likely to see improved system reliability and monitoring efficiency.
38 citations
TL;DR: In this article, sea level elevation and salinity were simulated during flood and ebb currents using nonlinear numerical models for both inlets, and it was found that the Cuautla Canal contributed to the deterioration of the once Laguncularia racemosa dominated forests, which is slowly being replaced by Avicennia germinans, Rhizophora mangle, and extensive hypersaline floodplains.
Abstract: The mangrove-estuarine system of Marismas Nacionales, Mexico is considered the most extensive wetland complex of the eastern Pacific coast. Originally, this large wetland was connected to the ocean solely through a natural inlet (Teacapan). However, in the early 1970s, it was decided that an artificial inlet (Cuautla Canal) will provide a second direct connection to the ocean that could help enhance local economic development. Unfortunately, it is believed that hydrological modification resulting from this inlet changed the hydrodynamics and thus massive loss of mangroves. Hence, the purpose of this investigation was to assess the tidal hydrodynamics before and after the canal’s construction and thus understand the potential negative impacts of such unsupervised coastal projects. Specifically, sea level elevation and tidal circulation velocities were simulated during flood and ebb currents using nonlinear numerical models for both inlets. Results indicated that sea level elevation and salinity increased from 2 to 35 cm and 0.5 to 35 PSU in the Agua Brava lagoon, respectively. Additionally, there was an overall increase of 0.6 m/s regarding the tidal current velocities, and thus it is probable that the Cuautla Canal contributed to the deterioration of the once Laguncularia racemosa dominated forests, which is slowly being replaced by Avicennia germinans, Rhizophora mangle, and extensive hypersaline floodplains. Consequently, such modeling could help in mitigating the impacts of future coastal developments in Mexico or elsewhere by helping in the prediction of the possible influence of tidal hydrodynamic changes on the subtropical coastal vegetation.
11 citations