Janne Lahtinen

Microbiological quality and shelf-life of vacuum-packaged 'gravad' rainbow trout stored at 3 and 8 °C

Microbiological and sensory changes of vacuum-packaged ‘gravad’ rainbow trout slices were studied during storage at 3 and 8 °C. At the time of spoilage, after 27 and 20 days of storage at 3 and 8 °C, respectively, both mesophilic viable counts (MVC) and psychrotrophic viable counts (PVC) reached 106–107cfu/g at 3 °C and 107–108 cfu/g at 8 °C. H2S-producing bacteria constituted a high proportion of the PVCs and lactic acid bacteria (LAB) counts were lower than the other determined bacterial counts. Sensory scores decreased with increasing MVC and PVC. The judges considered samples unfit for human consumption at MVC and PVC levels exceeding 106 and 107 cfu/g for samples stored at 3 and 8 °C, respectively. At respective levels of 107 and 108 cfu/g, most of the samples were deemed unfit. The main reasons for sensory rejection at both storage temperatures were the lack of the typical product odour or an ammonia off-odour and colour change to dark violet. The shelf-lives of the rainbow trout slices based on microbiological and sensory analyses were 20 days and 18 days at 3 and 8 °C, respectively.

A calibration method for fully polarimetric microwave radiometers

A technique for absolute end-to-end calibration of a fully polarimetric microwave radiometer is presented. The technique is based on the tripolarimetric calibration technique of Gasiewski and Kunkee, but is extended to provide a means of calibrating all four Stokes parameters. The extension is facilitated using a biaxial phase-retarding microwave plate to provide a precisely known fourth Stokes signal from the Gasiewski-Kunkee (GK) linearly polarized standard. The relations needed to determine the Stokes vector produced by the augmented standard are presented, and the effects of nonidealities in the various components are discussed. The application of the extended standard to determining the complete set of radiometer constants (the calibration matrix elements) for the National Oceanic and Atmospheric Administration Polarimetric Scanning Radiometer in a laboratory environment is illustrated. A calibration matrix inversion technique and error analysis are described, as well. The uncertainties associated with practical implementation of the fully polarimetric standard for spaceborne wind vector measurements are discussed relative to error thresholds anticipated for wind vector retrieval from the U.S. National Polar-Orbiting Environmental Satellite System.

Recommended Terminology For Microwave Radiometry

We present recommended definitions for common terms in microwave remotesensing radiometry. Terms are grouped into three chapters: General Terminology, RealAperture Radiometers, and Polarimetric Radiometry. An alphabetical index lists the terms that are defined and the chapters in which the definitions are located.

Fully polarimetric microwave radiometer for remote sensing

The design, characteristics, and operation of the Helsinki University of Technology Fully Polarimetric Radiometer (FPoR) are described. The developed 36.5-GHz radiometer can be used for airborne remote sensing; however, ground-based and laboratory measurements are also possible. A direct cross-correlation technique with analog correlators, which measures all four Stokes parameters simultaneously, is applied. This paper is the first successful demonstration of an analog direct cross-correlation technique for polarimetric remote sensing radiometry. The radiometer was subjected to a variety of laboratory tests, and considerable attention is given to analysis of the characteristics of the instrument. Owing to the effective active temperature control system of the receiver, the radiometric stability of the instrument was found to be very high; test results showing stabilities below 10 mK and of 4-40 mK on time scales of 800 and 8000 s, respectively, are presented. Furthermore, the absolute accuracy of the system is analyzed to be at a sub-Kelvin level for most measurement conditions. A maritime wind vector experiment was carried out over the Gulf of Finland. The feasibility and performance of the applied correlation technique and the whole radiometer system were verified for fully polarimetric airborne measurements. The obtained brightness temperatures of the first three Stokes parameters show typical harmonic behavior with respect to the surface wind; the results suggest, however, that the model coefficients presented earlier for oceans may not be directly applicable for different conditions.

SMOS Calibration Subsystem

Interferometric radiometry is a novel concept in remote sensing that is also presenting particular challenges for calibration methods. In this paper, we describe the calibration subsystem (CAS) developed for the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS) interferometer of the Soil Moisture and Ocean Salinity (SMOS) satellite. CAS is important for the overall performance of the payload as it calibrates out the differences between the multiple receivers of MIRAS. SMOS is in the final phase of development and is due to launch in 2008.

HUT fully polarimetric calibration standard for microwave radiometry

This paper describes the Helsinki University of Technologys Fully Polarimetric Calibration Standard (FPCS). The developed standard generates a complete Stokes reference vector and it is applied for the end-to-end absolute calibration of a fully polarimetric microwave radiometer at 36.5 GHz. The FPCS is based on the function principle of a Gasiewski-Kunkee linearly polarized (tripolarimetric) standard, with an additional phase retardation plate to generate the fourth Stokes parameter. Design considerations and operational aspects of the standard are discussed in this paper. An advanced calibration procedure, which takes advantage of both the tripolarimetric and fully polarimetric calibration scenes to suppress calibration uncertainties, is introduced. The feasibility of the standard has been verified and the generated brightness temperatures in a sample calibration are presented. An extensive set of tests has been performed to evaluate the characteristics and performance of the calibration standard. Furthermore, the use of the advanced calibration procedure to measure the characteristics of the phase retardation plate has been successfully demonstrated. The achievable calibration accuracy is analyzed and discussed relative to requirements for maritime wind vector measurements; the results indicate that the pixel-to-pixel retrieval of the wind speed is possible with high accuracy and the retrieval of the wind direction with at least moderate accuracy. In addition to calibration of a fully polarimetric radiometer, other potential applications, e.g., linearity measurements, are discussed.

Comparison of analog continuum correlators for remote sensing and radio astronomy

Two different designs of analog correlators for radiometry are compared in this paper. A continuum correlator based on a microwave nonlinear device is a simple and inexpensive way to detect wide-band polarized signals. Analysis and extensive measurements including linearity, dynamic range, amplitude response, phase balance, and stability are presented, and the suitability of the designs for microwave radiometry is discussed. Both correlators showed nearly ideal performance. A novel method for determining the correlator degradation factor is applied.

Fabrication and Characterization of Large Free-Standing Polarizer Grids for Millimeter Waves

Construction of large aperture free-standing metal wire grids is demonstrated for the lower end of the millimeter wave spectral region. For the constructed two grids the co-polarized and cross-polarized components of transmitted power were measured at 45° oblique incidence. The measurements were performed as a function of wire orientation angle and in more detail at selected angles. The results are in good agreement with the theoretical results presented in the literature. In order to save time and costs the construction apparatus was simplified from those reported previously by other authors. It was shown that for this frequency range the grid characteristics are not degraded when such an apparatus is applied. One of the constructed grids will be used in a calibration system of the Helsinki University of Technology (HUT) polarimetric radiometer.

Reference Radiometer of SMOS: Development and Calibration

Three Flight Models (FM) of the reference ra- diometer of European Space Agencys SMOS mission have been developed and tested. SMOS stands for Soil Moisture and Ocean Salinity. The reference radiometer is a Noise Injection Radiometer and hence named as NIR; the NIR FMs have been developed by Elektrobit Microwave Ltd. in collaboration with Laboratory of Space Technology of Helsinki University of Technology, which has acted as a subcontractor. The NIRs will be integrated into the MIRAS (Microwave Imaging Radiometer Using Aperture Synthesis) payload in 2006. The MIRAS is the sole instrument onboard SMOS satellite. MIRAS has 66 regular receiver units (called LICEF) and three NIR units. The purpose of NIR subsystem is (1) to provide precise measurement of the average brightness temperature scene for absolute calibration of the MIRAS image map, (2) to measure the noise temperature level of internal active calibration sources for individual receiver calibration (named Calibration Subsystem, CAS), and (3) to form interferometer baselines, so-called mixed baselines, with the regular receiver units. The performance of the NIR is a decisive factor of the overall MIRAS performance. In this paper we present the design of the NIR flight models, the test campaign results, and both ground and orbital calibration techniques including the ground calibration results.

Reference radiometer for interferometric radiometry from space

The Noise Injection Radiometer (NIR) for SMOS mission is described. The Engineering Model (EM) of NIR has been developed, qualified, and characterized; results are presented in this paper.