Reconstruction of signal phases for signals closer than the DFT frequency resolution

Radar signal processing is a promising tool for vital sign monitoring. For contactless observation of breathing and heart rate a precise measurement of the distance between radar antenna and the patient's skin is required. This results in the need to detect small movements in the range of 0.5 mm and below. Such small changes in distance are hard to be measured with a limited radar bandwidth when relying on the frequency based range detection alone. In order to enhance the relative distance resolution a precise measurement of the observed signal's phase is required. Due to radar reflections from surfaces in close proximity to the main area of interest the desired signal of the radar reflection can get superposed. For superposing signals with little separation in frequency domain the main lobes of their discrete Fourier transform (DFT) merge into a single lobe, so that their peaks cannot be differentiated. This paper evaluates a method for reconstructing the phase and amplitude of such superimposed signals.

Polar Mesosphere Winter Echoes and their relation to infrasound

<p>Polar Mesosphere Winter Echoes (PMWE) are radar echoes that originate from the mesosphere at 50-80 km altitude and are observed with VHF radars during equinox and winter seasons. Strong PMWE are relatively rare phenomena, in most cases they are observed when the lower ionosphere displays high ionisation. Interpretations of observational results concerning PMWE are controversial and the origin of the echoes is still under debate. Especially intriguing is that in some cases of strong PMWE, the measured horizontal speeds of the radar reflecting structures can exceed 300 m/s. Radar reflection (scattering) by infrasound waves at frequencies below about 2 Hz was suggested in order to explain these observations. We will give recent examples of PMWE events of high horizontal speed as observed with the 52 MHz MST radar (ESRAD) located at Esrange (68°N, 21ºE) in northern Sweden. Together with this we will analyse infrasound measurements made at ground-based stations near Kiruna (67.5°N, 20.13ºE) and at the infrasound station IS37 (69°N, 18ºE) in Norway during these events. We discuss prospective relations between PMWE and the microbaroms that are generated by ocean swell in the North Atlantic.</p>

Volcanic history in the Smythii basin based on SELENE radar observation

Elucidation of the subsurface structure in the Smythii basin on the moon is important for understanding lunar volcanic history. Two lava units (Units 1 and 2) cover this basin. The spatial subsurface structure below Unit 2 is unknown. We used SELENE/Lunar Radar Sounder data to identify four subsurface boundaries at 130, 190, 300, and 420 m depths. The radar is reflected at the paleo-regolith layer sandwiched among lava flows, which is supported by a simple radar reflection/transmission model. The spatial distribution of subsurface boundaries demonstrates the deposition of Unit 2 on the subsidence in Unit 1. A simple loading model explained the maximum depth of subsidence (~500 m) and indicated that lithospheric thickness in the Smythii basin was ~24 km at 3.95 Gya. The estimated growth rate of the lithosphere was ~60 km/Ga during 3.95 to 3.07 Gya. After the formation of the Smythii basin at ~4.11 Gya, Unit 1 and Unit 2 deposited with eruption rates of ~8.4 × 10−4 km3/yr by 3.95 Gya and ~7.5 × 10−6 km3/yr by 3.07 Gya respectively. The timing of decline in volcanic activity in the Smythii basin differs from that for the lunar nearside maria, indicating the diversity of volcanism in various lunar areas.

KARAKTERISASI STRUKTUR BAWAH PERMUKAAN TANAH PEKEBUNAN PADA KEBUN CONTOH POLITANI KUPANG MENGGUNAKAN METODE GEORADAR

Telah dilakukan penelitian pada lahan kebun contoh Politeknik Pertanian Negeri Kupang. Lahan inimemiliki luas 50 km2 dan didesain sebagai lahan contoh yang disediakan oleh pihak kampus, sebagai tempat pelaksanaan kegiatan praktikum oleh Dosen dan Mahasiswadalam menunjang perkembangan teknologi yang kreatif dan inovatif untuk meningkatkan produktivitas pertanian. Tujuan dilakukannya penelitian ini yaitu untuk mengindentifikasi tipe sedimen tanah di permukaan dan bawah permukaan berdasarkan interpretasi data georadar. Akuisisi datapada penelitian ini dilakukan pada dua lintasan pengukuran yaitu lintasan G1 dengan panjang lintasan 390 meter dan lintasan G2 dengan panjang lintasan 400 meter dengan arah lintasan Timur-Barat. Pengumpulan data georadar dilakukan dengan konfigurasi radar reflection profiling menggunakan transducer 200 MHz yang dilengkapi dengan receiver serta dilakukan pengambilan empat titik sampel tanah secara diagonal pada lokasi penelitian. Pada metode ini, pulsa elektromagnetik (radar) dipancarkan ke dalam tanah sehingga pulsa tersebut dapat diteruskan, dipantulkan dan dihamburkan oleh struktur lapisan tanah di bawah permukaan. Pulsa radar yang dipantulkan akan kembali ke permukaan tanah dan diterima oleh receiver yang telah dipasang di permukaan tanah. Pulsa yang terekam pada receiver inilah yang dapat diolah (prosessing) dan ditampilkan dalam bentuk rekaman pencitraan dua dimensi (2D) berupa penampang radargram. Hasil penelitian berdasarkan interpretasi penampang radargram pada lintasan G1 dan G2 menunjukkan bahwa tipe sedimen tanah pada kebun contoh Politani Kupang dari permukaan tanah sampai pada kedalaman kurang dari dua meter di bawah permukaan tanah merupakan lapisan sedimen tanah grumusol dan mediteran yang berbutir halus sampai kasar. Hasil analisis sifat fisika tanah pada lapisanpermukaan dan bawah permukaan pada kebun contoh Politani Kupang memenuhi tingkat kesuburan tanah.