SAR-Based Vibration Estimation Using the Discrete Fractional Fourier Transform

A vibration estimation method for synthetic aperture radar (SAR) is presented based on a novel application of the discrete fractional Fourier transform (DFRFT). Small vibrations of ground targets introduce phase modulation in the SAR returned signals. With standard preprocessing of the returned signals, followed by the application of the DFRFT, the time-varying accelerations, frequencies, and displacements associated with vibrating objects can be extracted by successively estimating the quasi-instantaneous chirp rate in the phase-modulated signal in each subaperture. The performance of the proposed method is investigated quantitatively, and the measurable vibration frequencies and displacements are determined. Simulation results show that the proposed method can successfully estimate a two-component vibration at practical signal-to-noise levels. Two airborne experiments were also conducted using the Lynx SAR system in conjunction with vibrating ground test targets. The experiments demonstrated the correct estimation of a 1-Hz vibration with an amplitude of 1.5 cm and a 5-Hz vibration with an amplitude of 1.5 mm

Reduction of Vibration-Induced Artifacts in Synthetic Aperture Radar Imagery

Target vibrations introduce nonstationary phase modulation, which is termed the micro-Doppler effect, into returned synthetic aperture radar (SAR) signals. This causes artifacts, or ghost targets, which appear near vibrating targets in reconstructed SAR images. Recently, a vibration estimation method based on the discrete fractional Fourier transform (DFrFT) has been developed. This method is capable of estimating the instantaneous vibration accelerations and vibration frequencies. In this paper, a deghosting method for vibrating targets in SAR images is proposed. For single-component vibrations, this method first exploits the estimation results provided by the DFrFT-based vibration estimation method to reconstruct the instantaneous vibration displacements. A reference signal, whose phase is modulated by the estimated vibration displacements, is then synthesized to compensate for the vibration-induced phase modulation in returned SAR signals before forming the SAR image. The performance of the proposed method with respect to the signal-to-noise and signalto-clutter ratios is analyzed using simulations. Experimental results using the Lynx SAR system show a substantial reduction in ghosting caused by a 1.5-cm 0.8-Hz target vibration in a true SAR image

REDUCTION OF VIBRATION-INDUCED ARTIFACTS IN SYNTHETIC-APERTURE-RADAR IMAGERY USING THE FRACTIONAL FOURIER TRANSFORM

ABSTRACT In synthetic aperture radar (SAR) images of objects exhibiting low-level vibrations are accompanied by localized artifacts, or ghost targets, caused by the micro-Doppler present in the returned SAR signals. Conventional Fourier-transformbased SAR processing techniques are not fit to remove ghosting effects prior to image formation due to the non-stationary nature of the returned signals from vibrating objects. Recently, a method based on the discrete fractional Fourier transform (DFrFT) has been developed for estimating the instantaneous vibration accelerations and vibrating frequencies from returned SAR signals. Here, a novel image de-ghosting algorithm for vibrating targets in SAR imagery is proposed by employing the DFrFT-based vibration-estimation algorithm. The proposed de-ghosting method is applied to SAR data collected by the Lynx SAR system. Experimental results show a substantial reduction in ghosting caused by a 1.5-cm amplitude, 0.8-Hz vibration present in a test target

Size at birth, gestational age and cortisol secretion in adult life: foetal programming of both hyper- and hypocortisolism?

Objective: Recent studies have suggested that lifelong programming of the hypothalamic–pituitary–adrenal (HPA) axis in utero is an important mechanism in explaining the link between small size at birth and adult cardiovascular disease. However, direct evidence from human birth cohorts has so far been contradictory. We set out to study reasons for this discrepancy by examining the relationship between adult HPA axis function and birthweight and body proportions at birth in a group of elderly subjects with detailed birth records.Design: Birth cohort study.Subjects: Four hundred and twenty-one men and women (mean age 69·5 years, range 65·1–75·8 years) born at term in Helsinki, Finland, during 1924–33, with body size and gestational age at birth recorded.Measurements: Fasting serum cortisol and cortisol-binding globulin concentrations. The concentration of free cortisol was estimated by their ratio.Results: There was no significant correlation between fasting cortisol concentrations and birthweight in either men or women. However, there was a weak inverse association between fasting cortisol and length at birth in women but not in men. There was also a significant positive association between cortisol and ponderal index in both genders. We found that the association between foetal growth on fasting total and free cortisol concentrations differed in subjects born at different gestational ages. In subjects born before 39 weeks of gestation, both total and free cortisol showed inverse correlations with birthweight (P = 0·02 and P = 0·09, respectively) and length at birth (P = 0·001 and P = 0·02), whereas in subjects born after 40 weeks of gestation there were positive correlations with birthweight (P = 0·06 and P = 0·002) and ponderal index at birth (P = 0·003 and P = 0·003). The interactions between birthweight and gestational age were statistically significant (P = 0·01 for total and P = 0·003 for free cortisol).Conclusions: These data suggest that the relationship between size at birth and cortisol concentrations in adult life is different in subjects born at different gestational ages: both hyper- and hypocortisolism may arise as a consequence of foetal programming of the hypothalamic–pituitary–adrenal axis during intrauterine life

Serum insulin-like growth factor (IGF)-I and IGF-binding protein-1 in elderly people: relationships with cardiovascular risk factors, body composition, size at birth, and childhood growth

The IGF system is important in regulation of fetal and childhood growth. In later life, IGF-I and IGF-binding protein-1 (IGFBP-1) have been implicated in the pathogenesis of arteriosclerosis. They are, thus, potential candidates in explaining the link between early growth and adult cardiovascular disease. We measured fasting serum IGF-I and IGFBP-1 concentrations in 394 men and women from a cohort of 7086 individuals, born between 1924 and 1933 in Helsinki, Finland, whose weight and height were recorded at birth and from 7 to 15 yr of age. They also underwent clinical examination, including measurement of body fat using bioimpedance, blood pressure, glucose tolerance, and plasma insulin and fibrinogen concentrations. Serum IGF-I was positively correlated with fasting glucose (r = 0.10, P = 0.06) and fibrinogen (r = 0.19, P = 0.0001) concentrations and blood pressure (systolic and diastolic r = 0.10, P 0.05) and inversely with percentage body fat (r = -0.13, P = 0.01) and waist circumference (r = -0.11, P = 0.03). IGFBP-1 was inversely correlated with adult body mass index (BMI) (r = -0.46, P &lt; 0.0001), fasting glucose and insulin concentrations, and blood pressure. There were correlations between the adult level of IGFBP-1 and birth weight (r = 0.11, P = 0.03) and ponderal index (weight/length3) at birth (r = 0.13, P = 0.01), but IGF-I was not related to birth measurements. There were interactive effects between childhood height or BMI and adult BMI on IGF-I and IGFBP-1 in adulthood. Tall height and high BMI at 7 yr were associated with low IGF-I (P = 0.03 for height and P = 0.003 for BMI) and high IGFBP-1 (P = 0.02 and P = 0.06) in adulthood but only in those subjects whose current BMI was below median. On further analysis these interactive effects were particularly strong for height in childhood and adult lean BMI (lean body mass/height2). Among men and women of below-average lean BMI, tall height at 7 yr was associated with low adult IGF-I (P = 0.007) and high IGFBP-1 (P = 0.0004) concentrations [interaction (7-yr height x adult lean BMI); P = 0.008 for IGF-I and 0.001 for IGFBP-1]. There is no evidence that reduced fetal growth programs IGF-I concentrations in old age. An association between small size at birth and low IGFBP-1 concentrations may in part reflect fetal programming effects on insulin resistance. Given the anabolic effects of the GH-IGF-I axis, subjects with tall height in childhood but low adult lean body mass may be at risk of late-life GH-IGF-I axis dysfunction. Prospective studies should address whether this group is susceptible to type 2 diabetes, coronary heart disease, and osteoporosis. This work was supported by grants from Academy of Finland, British Heart Foundation, Cancer Society of Finland, Finska Läkaresällskapet, Helsinki University Central Hospital Research Fund, The Foundation for Pediatric Research, Sigrid Jusélius Foundation, Sydäntutkimussäätiö, and National Institute of Child Development Grant 1-R01-HD41107-01 (to D.I.W.P.). <br/

Promoting Wellbeing in Pregnancy: A Multi-component Positive Psychology and Mindfulness-Based Mobile App

Pregnancy involves important changes for women of all ages: it is a time of physical and psychological change. Women may experience anxiety and negative emotions, which can negatively influence their wellbeing and make difficult their adaptation to the new role of mothers. Furthermore, poor mental well-being and difficulties in emotion regulation can negatively affect obstetric outcomes, development of the child and neonatal adaptation. The aim of this work is to present a new self-applied multi-component positive psychology- and mindfulness-based intervention (MPPMI) supported by a mobile App addressed to pregnant women. The core of this MPPMI is to combine traditional positive psychology activities with mindfulness-based exercises. The purpose of this MPPMI App (available in both Android and IOS versions) is to increase positive feelings, behaviors and cognitions and to learn strategies to better cope with anxiety to get adaptively and positively through pregnancy. The intervention is composed by five modules, for a total length of five weeks, and each module includes three activities. The future steps will be to carry out a pilot study to examine the program implementation and preliminary evaluate the effectiveness of the intervention on women\u2019s mental well-being, both at the end of the intervention and after childbirth