Simo Tauriainen

A semi-operative approach to lake water quality retrieval from remote sensing data

A semi-operative approach to retrieve chlorophyll-a concentration from airborne/spaceborne spectrometer observations has been developed and tested using the airborne imaging spectrometer (AISA) data from 11 lakes located in southern Finland. The retrieval approach is empirical and requires nearly simultaneous in situ training data on water quality for the determination of regression coefficients. However, the training data does not have to be collected from every lake under investigation. Instead, the results obtained indicate that reliable estimates on the level of chlorophyll-a (chl-a) for an individual lake can be achieved without employing in situ data representing this specific lake. This enables the estimation of water quality from remotely sensed data for numerous lakes with the aid of reference data only for a few selected lakes representing the region under investigation. In addition, it is shown that the remotely sensed spectrum shape characteristics are highly affected by the trophic and humic state of the lake water.

First 2-D Interferometric Radiometer Imaging of the Earth From an Aircraft

The Helsinki University of Technology has recently finished the construction of a 2-D airborne aperture synthesis radiometer and conducted a successful test flight with the complete instrument. During the test flight, a number of different brightness temperature sources were measured to examine the instruments stability, electromagnetic compatibility issues, calibration methods, and image reconstruction algorithm. A set of images from this first test flight is presented, and their main features are discussed

MIRAS reference radiometer: a fully polarimetric noise injection radiometer

A prototype reference radiometer for the Microwave Imaging Radiometer Using Aperture Synthesis (MIRAS) instrument of the Soil Moisture and Ocean Salinity satellite has been developed. The reference radiometer is an L-band fully polarimetric noise injection radiometer (NIR). The main purposes of the NIR are: 1) to provide precise measurement of the average fully polarimetric brightness temperature scene for absolute calibration of the MIRAS image map and 2) to measure the noise temperature level of the noise distribution network of the MIRAS for individual receiver calibration. The performance of the NIR is a decisive factor of the MIRAS performance. In this paper we present the operation principles and calibration procedures of the NIR, a measurement technique called blind correlation making measurements of full Stokes vector possible with the noise injection method, and finally experimental results verifying certain aspects of the design.

A Comparison of Airborne Passive Microwave Brightness Temperatures and Snowpack Properties across the Boreal Forests of Finland and Western Canada

The seasonal snowpack across the boreal forest is an important national resource in both Canada and Finland, contributing freshwater for agriculture, human consumption, and hydropower generation. In both countries, satellite passive microwave data are utilized to provide operational information on snow depth and snow water equivalent (SWE) throughout the snow cover season. Airborne passive microwave surveys conducted independently across Finland and western Canada during March and April 2005 and March 2006 provided the opportunity to assess the level of similarity in snowpack physical properties and brightness temperature response to snowpack qualities using two independent data sets. The primary objectives of these campaigns were to determine the influence of small-scale heterogeneity on satellite data, using relatively high resolution airborne measurements, and to assess the Helsinki University of Technology (HUT) snow emission model capability of predicting emitted brightness temperatures under varying snowpack and landscape conditions. Comparisons of brightness temperature emissions over different land cover types showed a clear distinction of wetlands and snow-covered ice from forested and open areas. This is reflected also as a strong relationship between 6.9-GHz measurements and fractional lake cover in both Canada and Finland, with relationships at 18 and 37 GHz being less consistent between data sets. Comparisons of experimental data versus HUT snow emission model predictions showed relatively good agreement between the simulations and airborne data, specifically for the Finnish data set.

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.

AMIRAS—An Airborne MIRAS Demonstrator

This paper describes AMIRAS, an airborne demonstrator of the Microwave Imaging Radiometer with Aperture Synthesis, which is the instrument onboard ESAs Soil Moisture and Ocean Salinity (SMOS) mission. The main electrical, mechanical, thermal, and control elements of the demonstrator are shown, together with its capabilities and performances as demonstrator of the spaceborne instrument. AMIRAS main tests inside an anechoic chamber, field ground experiments, and its first two maiden flights are reported, and some results of these tests are highlighted. AMIRAS will further be used in some calibration and validation campaigns of the SMOS mission.

The Helsinki University of Technology/Ylinen Electronics airborne L-band interferometric radiometer

An airborne L-band two-dimensional interferometric radiometer by aperture synthesis, HUT-2D, is under development and construction at LST/HUT (Laboratory of Space Technology/Helsinki University of Technology) in co-operation with Ylinen Electronics Ltd. The instrument consists of 36 antenna/receiver elements and an FPGA-based digital correlator and it will be accommodated onboard the LST/HUT remote sensing aircraft, Short SC-7 Skyvan.

Helsinki University of Technology Synthetic Aperture Radiometer -HUT-2D

Helsinki University of Technology (TKK), Laboratory of Space Technology has developed an airborne two dimensional synthetic aperture radiometer for remote sensing purposes. The radiometer - called HUT-2D - measures the ground target using L-band channel reserved for radio astronomy. Main interests are in soil moisture (SM) and sea surface salinity (SSS) monitoring. The instrument is similar with the European Space Agencys (ESA) SMOS (Soil Moisture and Ocean Salinity) mission MIRAS (Microwave Imaging Radiometer by Aperture Synthesis) instrument. The HUT-2D instrument will be used in SMOS mission calibration and validation activities. Already, the development work of the HUT-2D instrument has given valuable information to the SMOS project. This paper describes the instrument and presents example airborne measurements in Finnish coastal zone.

MIRAS Airborne Demonstrator

This paper presents the MIRAS Airborne Demonstrator, a prototype instrument for the MIRAS radiometer onboard the SMOS mission. A description of the instrument is given, the first results of its performances and the planned follow on activities to be done

Airborne ocean wind vector measurement using 36.5 GHz profiling polarimetric radiometer

An airborne fully polarimetric 36.5 GHz profiling radiometer has been developed in the Laboratory of Space Tech- nology of the Helsinki University of Technology. The radiometer has been used for airborne measurements of the wind vector over the Gulf of Finland. A series of measurements have been conducted over a period of two years; the results are presented in this paper. The Fourier coefficients of the harmonics of the first three Stokes parameters have been solved and their behaviour as a function of the measurement incidence angle and the wind speed has been examined. We show a clear relationship between the incidence angle and the harmonics of the third Stokes parameter, something that is not presented before. Furthermore, based on our analysis we show a relationship between the wind speed and the three Stokes parameters taking also the incidence angle into account. I. INTRODUCTION The maritime wind vector retrieval using a fully polarimetric radiometer has been one of the key points of interest in passive microwave remote sensing as of early 1990s. The sensitivity of sea surface brightness temperatures to ocean wind speed and direction has been demonstrated in many studies. The resuls presented in this paper were obtained with the airborne fully polarimetric radiometer developed in HUT; it measures the so-called modified Stokes parameters, which are defined under the Rayleigh-Jeans approximation as (1):