References of "Ejigu, Yohannes Getachew"
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See detailTracking Hurricanes using GPS atmospheric precipitable water vapor field
Ejigu, Yohannes Getachew; Teferle, Felix Norman UL; klos, Anna et al

in Beyond 100: The Next Century in Geodesy (2020)

Tropical cyclones are one of the most powerful severe weather events that produce devastating socioeconomic and environmental impacts in the areas they strike. Therefore, monitoring and tracking of the ... [more ▼]

Tropical cyclones are one of the most powerful severe weather events that produce devastating socioeconomic and environmental impacts in the areas they strike. Therefore, monitoring and tracking of the arrival times and path of the tropical cyclones are extremely valuable in providing early warning to the public and governments. Hurricane Florence struck the East cost of USA in 2018 and offers an outstanding case study. We employed Global Positioning System (GPS) derived precipitable water vapor (PWV) data to track and investigate the characteristics of storm occurrences in their spatial and temporal distribution using a dense ground network of permanent GPS stations. Our findings indicate that a rise in GPS-derived PWV occurred several hours before Florence’s manifestation. Also, we compared the temporal distribution of the GPS-derived PWV content with the precipitation value for days when the storm appeared in the area under influence. The study will contribute to quantitative assessment of the complementary GPS tropospheric products in hurricane monitoring and tracking using GPS-derived water vapor evolution from a dense network of permanent GPS stations [less ▲]

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See detailTracking hurricanes Harvey and Irma using GPS tropospheric products
Ejigu, Yohannes Getachew; Teferle, Felix Norman UL; Hunegnaw, Addisu UL et al

Poster (2019, December 10)

The 2017 Hurricanes season was one of the most powerful severe weather events producing catastrophic socio-economic and environmental effects on the east coast of the United States. Therefore, tracking ... [more ▼]

The 2017 Hurricanes season was one of the most powerful severe weather events producing catastrophic socio-economic and environmental effects on the east coast of the United States. Therefore, tracking their path accurately is extremely useful. Today Global Navigation Satellite Systems (GNSS) tropospheric products, such as Zenith Wet Delays (ZWD), and Integrated Water Vapor (IWV) are used as complementary data sets in Numerical Weather Prediction (NWP) models. In this study, we employed GPS-derived IWV and horizontal tropospheric gradient information to monitor and investigate the complicated characteristics of hurricane events in their spatial and temporal distribution using a dense ground network of GPS stations. Our results show that a surge in GPS-derived IWV occurred several hours prior to the manifestation of the major hurricanes Harvey and Irma. We used the derived GPS-derived IWV information as input to spaghetti lines weather models, allowing us to predict the paths of Harvey and Irma hurricanes. As such, a parameter directly estimated from GPS can provide an additional resource for improving the monitoring of hurricane paths [less ▲]

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See detailImproved Monitoringand Tracking Hurricanes using GPS Atmospheric WaterVapour
Ejigu, Yohannes Getachew; Teferle, Felix Norman UL; klose, Anna et al

Poster (2019, April 09)

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See detailImpact of GPS Antenna Phase Center Models on Zenith Wet Delay and Tropospheric Gradients
Ejigu, Yohannes Getachew; Hunegnaw, Addisu UL; Abraha, Kibrom Ebuy UL et al

in GPS Solutions (2019), 23(5),

We demonstrate the potential for the Global Positioning System (GPS) to provide highly accurate tropospheric products for use in meteorological applications. Tropospheric products, in particular the wet ... [more ▼]

We demonstrate the potential for the Global Positioning System (GPS) to provide highly accurate tropospheric products for use in meteorological applications. Tropospheric products, in particular the wet delays, are treated as an unknown parameter in GPS processing and are estimated with other parameters such as station coordinates. In this study, we investigate the effects of Phase Center Correction (PCC) models on tropospheric zenith wet delay (ZWD), integrated water vapor (IWV) and gradient products. Two solutions were generated using the GAMIT software over the EUREF Permanent GNSS Network (EPN). The first (reference) solution was derived by applying the International GNSS Service (IGS) type-mean PCC model, while for the second solution PCC models from individual calibrations were used. The solutions were generated identically, except for the PCC model differences. The two solutions were compared, with the assumption that common signals are differenced out. The comparison of the two solutions clearly shows a bias in all tropospheric products, which can be attributed to PCC model deficiencies. Overall, mean biases of ±1.8, ±0.3, ±0.14 and ±0.19 mm are evident in ZWD, IWV, North-South and East-West gradients, respectively. Moreover, the differences between the two solutions show seasonal variations. For all antenna types, the ZWD and IWV differences are dominated by white plus power-law noise, with latter characterizing the low-frequency spectrum. On the other hand, the horizontal gradients exhibit a white plus first order autoregressive noise characteristic with less than 1% white noise. The individual PCC model provides a better fit to an external independent model in terms of gradient estimate and also provides up to 3 % more carrier phase ambiguity resolution. [less ▲]

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