RESUMO
Little is known about the vocalizations of Irrawaddy dolphins (Orcaella brevirostris) in the Gulf of Thailand. The present study first described the echolocation clicks of Irrawaddy dolphins in Trat Bay, in the eastern Gulf of Thailand, using a broadband hydrophone system. Over 2 h of acoustic recordings were collected during 14-day study periods in December 2017 and December 2018. Several criteria were used to judge if a click was on axis or as close to the acoustic axis as possible. To calculate the distance of dolphins, a low-budget localization method based on arrival time differences between the direct and indirect signals was used in the present study. The clicks had a mean peak-to-peak source level of 192 ± 3 dB re 1 µPa, an energy flux density source level of 131 ± 3 dB re 1 µPa2s, a mean centroid frequency of 98 ± 10 kHz, a mean duration of 16 ± 2 µs, and a -3 dB bandwidth of 79 ± 13 kHz. The click parameters of the Irrawaddy dolphins in Trat Bay were slightly different from the clicks recorded from the dolphins in Sundarbans, Bangladesh. The present study provided a basic description of the click characteristics of Irrawaddy dolphins in Trat Bay, which could contribute to the management and conservation strategies for local Irrawaddy dolphins, and a basic reference for the proper input parameters in passive acoustic monitoring and detection.
Assuntos
Comportamento Animal/fisiologia , Ecolocação/fisiologia , Vocalização Animal/fisiologia , Acústica , Animais , Golfinhos , Espectrografia do Som/métodos , TailândiaRESUMO
The effective management and utilization of resources and ecological environment of coastal wetland require investigation and analysis in high precision of the fractional vegetation cover of invasive species Spartina alterniflora. In this study, Sansha Bay was selected as the experimental region, and visible and multi-spectral images obtained by low-altitude UAV in the region were used to monitor the fractional vegetation cover of S. alterniflora. Fractional vegetation cover parameters in the multi-spectral images were then estimated by NDVI index model, and the accuracy was tested against visible images as references. Results showed that vegetation covers of S. alterniflora in the image area were mainly at medium high level (40%-60%) and high level (60%-80%). Root mean square error (RMSE) between the NDVI model estimation values and true values was 0.06, while the determination coefficient R2 was 0.92, indicating a good consistency between the estimation value and the true value.
