Synthetic Aperture Microwave Radiometer Research Articles

Sea surface temperature retrieval based on simulated space-borne one-dimensional multifrequency synthetic aperture microwave radiometry

The space-borne one-dimensional multifrequency synthetic aperture microwave radiometer (1D-MSAMR) offers new possibilities for detecting high spatial resolution sea surface temperature (SST). To achieve higher SST retrieval accuracy, an SST retrieval algorithm, the two-step retrieval algorithm (TSSR), is proposed based on the multiple linear regression (MLR) algorithm. In this study, we investigated the SST retrieval accuracy of 1D-MSAMR based on simulation experiments. For the study, we assumed that the frequencies of the 1D-MSAMR were 6.9, 10.65, 18.7, 23.8, and 36.5 GHz, and that all frequencies worked in a dual polarization (vertical and horizontal) manner. We used an ocean-atmosphere microwave radiation brightness temperature model and the 1D-MSAMR simulator to simulate the measured brightness temperature based on WindSat data provided by the Remote Sensing Systems (RSS). An MLR algorithm and the TSSR were then developed to retrieve the SST within the incidence angle range of 0°–65°. The results show that the SST retrieval errors of the two SST retrieval algorithms decreased with the increase of incidence angle. The TSSR had higher retrieval accuracy, especially at low incidence angle. The average retrieval accuracy of the TSSR was about 0.3 K higher than that of the MLR algorithm. The retrieval error of the TSSR was also less sensitive to the measurement error of the 6.9 GHz frequency than the MLR algorithm.

Design of multi-channel digital correlator in SAMR

Synthetic Aperture Microwave Radiometer (SAMR) can be carried on the satellite to realize the global large-scale measurement of ocean salinity and soil moisture. As a key component of SAMR, the multi-channel digital correlator has been introduced in this paper from three aspects: an improved method to implement multi-channel correlation, the correlator design and the test results of the correlator. The improved method which effectively reduces the FPGA resource utilization and system complexity is applied to the multi-channel digital correlator system which consists of three signal collectors and one signal processor. The design of multi-channel digital correlator can ensure the real-time signal sampling and processing of 144 ADC channels. The results demonstrate that the measurement accuracy of correlation coefficient can exceed 0.99.

Sea surface temperature retrieval based on simulated microwave polarimetric measurements of a one-dimensional synthetic aperture microwave radiometer

Sea surface temperature retrieval based on simulated microwave polarimetric measurements of a one-dimensional synthetic aperture microwave radiometer

Estimation of marine winds in and around typhoons using multi-platform satellite observations: Application to Typhoon Soulik (2018)

Estimating horizontal winds in and around typhoons is important for improved monitoring and prediction of typhoons and mitigating their damages. Here, we present a new algorithm for estimating typhoon winds using multiple satellite observations and its application to Typhoon Soulik (2018). Four kinds of satellite remote sensing data, along with their relationship to typhoon intensity, derived statistically from hundreds of historical typhoon cases, were merged into the final product of typhoon wind (MT wind): 1) geostationary-satellite-based infrared images (IR wind), 2) passive microwave sounder (MW wind), 3) feature-tracked atmospheric motion vectors, and 4) scatterometer-based sea surface winds (SSWs). The algorithm was applied to two cases (A and B) of Typhoon Soulik and validated against SSWs independently retrieved from active microwave synthetic aperture radar (SAR) and microwave radiometer (AMSR2) images, and vertical profiles of wind speed derived from reanalyzed data and dropsonde observations. For Case A (open ocean), the algorithm estimated the realistic maximum wind, radius of maximum wind, and radius of 15 m/s, which could not be estimated using the reanalysis data, demonstrating reasonable and practical estimates. However, for Case B (when the typhoon rapidly weakened just before making landfall in the Korean Peninsula), the algorithm significantly overestimated the parameters, primarily due to the overestimation of typhoon intensity. Our study highlights that realistic typhoon winds can be monitored continuously in real-time using multiple satellite observations, particularly when typhoon intensity is reasonably well predicted, providing timely analysis results and products of operational importance.

A Multiple Linear Regression Algorithm for Sea Surface Temperature Retrieval by One-Dimensional Synthetic Aperture Microwave Radiometry

AbstractOne-dimensional synthetic aperture microwave radiometer (1D-SAMR) can provide remote sensing images at a higher spatial resolution than those from traditional real aperture microwave radiometers. As 1D-SAMR operates at multiple incidence angles, we proposed a multiple linear regression method to retrieve sea surface temperature at an incidence angle between 0° and 65°. Assuming that a 1D-SAMR operates at various frequencies (i.e., 6.9, 10.65, 18.7, 23.8 and 36.5 GHz), a radiation transmission forward model was developed to simulate the brightness temperature measured by the 1D-SAMR. The sensitivity of the five frequencies to sea surface temperature was examined, and we evaluated the reliability of the regression method proposed in this study. Furthermore, 11 schemes with various frequency combinations were applied to retrieve sea surface temperature. The results showed that the five-frequency combination scheme performed better than the other schemes. This study also found that the accuracy of retrieved sea surface temperature is dependent on incidence angles. Finally, we suggested that the incidence angle range of the 1D-SAMR is necessary to be 30°–60° based on the relationship between the accuracy of retrieved sea surface temperature and the incidence angles.

Research on sea surface temperature retrieval by the one-dimensional synthetic aperture microwave radiometer, 1D-SAMR

Due to the low spatial resolution of sea surface temperature (TS) retrieval by real aperture microwave radiometers, in this study, an iterative retrieval method that minimizes the differences between brightness temperature (TB) measured and modeled was used to retrieve sea surface temperature with a one-dimensional synthetic aperture microwave radiometer, temporarily named 1D-SAMR. Regarding the configuration of the radiometer, an angular resolution of 0.43° was reached by theoretical calculation. Experiments on sea surface temperature retrieval were carried out with ideal parameters; the results show that the main factors affecting the retrieval accuracy of sea surface temperature are the accuracy of radiometer calibration and the precision of auxiliary geophysical parameters. In the case of no auxiliary parameter errors, the greatest error in retrieved sea surface temperature is obtained at low TS scene (i.e., 0.710 6 K for the incidence angle of 35° under the radiometer calibration accuracy of 0.5 K). While errors on auxiliary parameters are assumed to follow a Gaussian distribution, the greatest error on retrieved sea surface temperature was 1.330 5 K at an incidence angle of 65° in poorly known sea surface wind speed (W) (the error on W of 1.0 m/s) over high W scene, for the radiometer calibration accuracy of 0.5 K.

Retrieval of Sea Surface Wind Speed by One-Dimensional Synthetic Aperture Microwave Radiometer

Retrieval of Sea Surface Wind Speed by One-Dimensional Synthetic Aperture Microwave Radiometer

Bohai Sea Ice Parameter Estimation Based on Thermodynamic Ice Model and Earth Observation Data

We estimate two essential sea ice parameters—namely, sea ice concentration (SIC) and sea ice thickness (SIT)—for the Bohai Sea using a combination of a thermodynamic sea ice model and Earth observation (EO) data from synthetic aperture radar (SAR) and microwave radiometer. We compare the SIC and SIT estimation results with in-situ measurements conducted in the study area and estimates based on independent EO data from near-infrared/optical instruments. These comparisons suggest that the SAR-based discrimination between sea ice and open-water works well, and areas of thinner and thicker ice can be distinguished. A larger comprehensive training dataset is needed to set up an operational algorithm for the estimation of SIC and SIT.

Optic real-time signal processing for synthetic aperture microwave radiometer

Optic real-time signal processing for synthetic aperture microwave radiometer

Synthetic Aperture Microwave Radiometer and Image Retrieval

In this paper, the principle of synthetic aperture microwave radiometer (SARad) is introduced. The differences between SARad for earth observation and its parentage in radio astronomy, the synthetic aperture radio telescope, are analyzed, which results in two key technologies of SARad: the design of baseline combination and the image retrieval algorithm. In this paper, the general relationship between the output of an interfe rometer , which is called the visibility function or the spatial frequency sampling, and the baseline parameters is presented. The general formulation of visibility function and functional expression of the brightness temperature distribution from retrieved from visibility function are derived. Some discussions on the image retrieval and numerical simulations are given.

Mechanism and Preliminary Experiments of a L-Band Synthetic Aperture Microwave Radiometer

In this paper, prototype of a two-channel L-band interferometric synthetic aperture microwave radiometer, which is infect a two-element microwave interferometer, is designed and developed. The correlation experiment is conducted. Results of the experiment show that phase difference can be exactly retrieved with the complex correlator, which can be a core component of a synthetic aperture radiometer.

Airborne Synthetic Aperture Radiometer image and Optical Data Fusion and Evaluation

Microwave radiometer image contains information of ground brightness temperature.For its low resolution and unclear object's shape, it is not convenient to be studied. Something like SAR, synthetic aperture microwave radiometer also has the characteristics that it can acquire images during day and night and with all weather conditions. Moreover, it has the ability to penetrate surface soil or vegetation under lower frequency region. Contrast to the radiometer image, the optical images have higher resolution and contain different information. To integrate some features of these two kinds of images, some transform schemes, such as intensity|hue|saturation (IHS), principal component analysis (PCA) and wavelet transform (WT), were applied to merge the airborne synthetic aperture microwave radiometer and ETM+ images. The experiments show that the wavelet based transform method not only can preserve the spectral information of ETM+ image well, but also can preserve the texture information from radiometer image. In conclusion, the WT approach has the best potential among those three methods.

A Wavelet Based Scattering Data Interpolation in Synthetic Aperture Microwave Radiomter

Soil moisture and ocean salinity are two important parameters for water cycle and climate change studies. The best way to measure these two parameters is to use microwave radiometer at low frequency band, such as P or L band. However, at these frequencies, the physical size of the antenna is very big in order to reach a modest spatial resolution. To scan such kind of large antenna is also difficult. Further more, if the antenna beam become very narrow, the integration time of each resolution cell will become small which will lead to poor measurement sensitivity.;To overcome all difficulties mentioned above, the synthetic aperture microwave radiometer technology is proposed. This technology uses both thinned array antenna and electrical scan. Therefore not only the large/heavy antenna aperture problem is solved, but also the integration time will not be related to the spatial resolution any more. It is therefore a very promising technology for low frequency band microwave radiometers and can be implemented for soil moisture and ocean salinity applications.;The basic concept of synthetic aperture radiometer is to measure spatial frequency of the scene instead of the image itself. The output of the spatial frequency is usually called the visibillity function (VF). While all the spatial frequency outputs or VF are measured, corresponding to all baselines with different length and orientation, the image of the scene is a mathematical transformation of the VF. ;This paper put forward an interpolation method based on wavelet transform, whose role is to give a modification to the Fourier image reconstruction arithmetic of 2|D microwave synthetic aperture radiometer.

Calculation of the spatial resolution of a synthetic aperture microwave radiometer

The synthetic aperture microwave radiometer (SAMR) has been proved to be an interesting system for the remote sensing of the earth from space with a high spatial resolution. This paper presents the formulas for computing the spatial resolution of the SAMR. Some practical examples are also presented, and it is proved that the spatial resolution becomes more inferior with the increment of the off-nadir angle.

Calibration of a synthetic aperture radiometer

Calibration algorithms for a synthetic aperture microwave radiometer are presented. The calibration is geared to Earth remote sensing applications and is demonstrated on an airborne prototype thinned array imager. Two approaches to the system calibration are presented. The first utilizes commonly available reference brightness temperature scenes, such as open water, and the second utilizes data collected on the antenna range. Both algorithms yield spatial response information which is cast in matrix form and inverted to obtain the image reconstruction formula. Experimental results are examined, and errors in some reconstructed images are linked to the present prototype antenna design. Algorithms for improving the synthesized antenna pattern sidelobe performance are also presented. In one solution, the pattern efficiency is optimized by minimizing the pattern outside a defined beam. In another solution, the patterns are matched to a desired model pattern by the method of least squared errors. Both techniques offer an attractive alternative to aperture weighting.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Initial Results In The Development Of A Synthetic Aperture Microwave Radiometer

A radiometer that measures the complex correlation of the voltage from pairs of antennas at many different baselines is being developed. Each baseline produces a sample point in the Fourier transform of the scene, and a map of the scene is obtained after all measurements have been made by inverting the transform. A substantial reduction in the antenna collecting area required compared to a conventional imaging radiometer can be obtained in this manner. An aircraft prototype being developed is a hybrid which uses real aperture antennas to obtain resolution along-track (stick antennas) and uses aperture synthesis to obtain resolution across-track. The prototype was flight-tested aboard the NASA P-3 in June 1988. During this flight a map was made of the Delmarva Peninsula south of NASA's Wallops Flight Facility. This initial map shows the major land/water features and compares very favorably with a Landsat image of the area, suggesting a bright outlook for the development of this technique in the future.