부산대학교 도서관

A new Cyclone Global Navigation Satellite System (CYGNSS) data product is described, which is generated from the raw intermediate frequency (IF) data. The product includes several established signal coherence detectors, including the power ratio ${P}_{\mathrm {ratio}}$ , complex zero-Doppler delay waveform, full entropy ${E}_{\mathrm {full}}$ , and a novel fast entropy detector ${E}_{\mathrm {fast}}$ . Both entropy detectors are provided with two temporal resolutions: 2 and 50 ms. Coherence performance is characterized using the phase derivative of the reflected signal at the peak of the delay waveform ${\varphi }_{\mathrm {peak}}$ . Threshold values of the full entropy detector are determined, which classify scattering into three regimes: incoherent, partially coherent, and coherent. Several scattered signal strength products are included: signal-to-noise ratio (SNR), reflected power ${P}_{g}$ , reflectivity ${\Gamma }$ , and normalized bistatic radar cross section (NBRCS). Each of these products is derived using a coherent integration time of ${T}_{c}$ = 1 ms and incoherent integration times of ${N}_{\mathrm {inc}}$ = 1000, 500, 250, 100, 50, and 2 ms. Signal strength time series at the shorter (2 and 50 ms) times provides excellent detection of land–water transitions in heterogeneous scenes. Delay Doppler maps (DDMs) are also generated with high delay ( ${\Delta \tau }$ = 1/16 chip) and Doppler ( ${\Delta f}$ = 50 Hz) resolution. The behavior of each signal strength product as a coherence detector is examined using the full entropy method as a reference. Performance is characterized using receiver operating characteristic (ROC) curves. The fast entropy method, which has a much lower computational cost, is similarly characterized. This suite of coherence detection methods can be used to detect the presence of small inland water bodies.