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ABSTRACT: L-band radiometry is widely considered the best technique for Earth observing satellites to measure sea surface salinity (SSS). Interferometric aperture synthesis is a new technology applicable in spaceborne remote sensing at low frequencies. The challenge of the technology comes with decreased radiometric resolution and complexity in calibration compared to conventional radiometer systems. Due to these issues and the overall newness of the concept, validation of the technology for salinity retrieval purposes is desired. In this paper, we describe an intense measurement campaign carried out with the complete interferometric aperture synthesis radiometer system HUT-2-D, designed and operated by the Helsinki University of Technology. The campaign aimed at the detection of a changing salinity level in the Baltic Sea, in the coastal areas of Finland. We describe the campaign comprising details of the ground truth collection, sea surface emission modeling, and radiometric data analysis. We have a special emphasis on the assessment of the impact of the sea state on the radiometric measurements, which is considered one of the major obstacles for SSS retrieval at the L-band. For this purpose, we present a new correlation between sea roughness information collected with the Global Navigation Satellite System reflectometer and radiometric data measured by an L-band radiometer system.
IEEE Transactions on Geoscience and Remote Sensing 12/2011; · 2.89 Impact Factor
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ABSTRACT: The launch of the European Space Agency's (ESA) Soil Moisture and Ocean Salinity (SMOS) satellite in November 2009 opened a new era in monitoring globally and continuously these two environmental parameters. The importance of these measurements to provide information on Earth's climate and its changes has been pointed out by the scientific community in recent years [1]. With SMOS data weather prediction models can be improved and extreme weather phenomena better understood. The SMOS payload radiometer called MIRAS (Microwave Imaging Radiometer using Aperture Synthesis) uses aperture synthesis technique, new to remote sensing, to form an image of the target [2]. The used technique is very effective in producing good quality data with reasonable ground resolution for passive L-band measurements. However, since it is based on having numerous individual receivers, from which the output signals are correlated, the technique is sensitive to artificial or man-made interfering signal sources. It is of great importance to identify the existing sources of RFI (Radio Frequency Interference) to ensure good quality data. This paper describes the work done in Aalto University in this field using available SMOS data and the Aalto University L-band aperture synthesis radiometer (HUT-2D) airborne data collected during the SMOS rehearsal campaigns and other national funded campaigns.
General Assembly and Scientific Symposium, 2011 XXXth URSI; 09/2011
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ABSTRACT: This paper describes the analysis of L-band radiometric measurement data gathered with the synthetic aperture radiometer HUT-2D during several ground-based and airborne measurement campaigns. The radiometric data are analyzed from the instrument's performance point of view, aiming to verify the theoretical performance of an instrument of this kind and to assess the performance of the HUT-2D radiometer system in particular. The data sets considered for the study consist of measurements of well-known natural targets, such as cosmic background radiation, and measurements of pure water scenes, the brightness temperature of which is possible to model based on in situ measurements. We define four figures of merit, which are applicable for synthetic aperture radiometers. These are radiometric resolution, image bias, pixel-to-pixel random error, and temporal stability. Then, we use the selected data sets to assess these in the case of HUT-2D. The experimental results are discussed and compared to the theoretical values, where applicable. Also, we discuss possibilities to improve the presented performance. The main results of this paper are the consolidated performance parameters of the HUT-2D instrument. We study and discuss the properties of the error components related to the technology in a general level, and study the scalability of the errors as a function of the measured targets. In particular, the stability of the direction-dependent error component is pointed out, and a mitigation guideline is proposed.
IEEE Transactions on Geoscience and Remote Sensing 03/2011; · 2.89 Impact Factor
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ABSTRACT: The successful launch of the European Space Agency's (ESA) Soil Moisture and Ocean Salinity (SMOS) satellite mission on November 2nd 2009 opened a new era of global monitoring with L-band passive microwave instruments. The main objective of the mission is to measure soil moisture and sea surface salinity globally. The sole payload of SMOS is the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS). In this paper we compare the first SMOS measurements over a sub-Arctic boreal forest area with tower-based and airborne reference data. Our main interest is the evolution of the boreal soil frost, since it has a large impact on the carbon cycle in the Arctic region.
Geoscience and Remote Sensing Symposium (IGARSS), 2010 IEEE International; 08/2010
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J. Kainulainen,
K. Rautiainen,
P. Sievinen,
J. Seppänen,
E. Rouhe,
M. Hallikainen,
J. Dall'Amico,
F. Schlenz,
A. Loew,
S. Bircher,
C. Montzka
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ABSTRACT: In this paper we present calibration and validation activities of European Space Agency's SMOS mission, which utilize airborne interferomentric L-band radiometer system HUT-2D of the Aalto University. During spring 2010 the instrument was used to measure three SMOS validation target areas, one in Denmark and two in Germany. We present these areas shortly, and describe the airborne activities. We show some exemplary measurements of the radiometer system and demonstrate the studies using the data.
Geoscience and Remote Sensing Symposium (IGARSS), 2010 IEEE International; 08/2010
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ABSTRACT: In this paper we present a preliminary analysis of the radiometric performance of the three 1.4 GHz Noise Injection Radiometers of the SMOS satellite. We assess the radiometric resolution and stability of the receivers, and the similarity between their measurements. The units aim at measurements of a common antenna temperature, which determines the overall brightness temperature level of SMOS retrievals. For this purpose, we use measurement data gathered during the first two months of the in-orbit operations of the satellite, which was launched in November 2009. The preliminary assessment of the abovementioned performance parameters shows that the units meet the requirements with a margin.
Microwave Radiometry and Remote Sensing of the Environment (MicroRad), 2010 11th Specialist Meeting on; 04/2010
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ABSTRACT: During the last two decades, the development of synthetic aperture radiometers for remote sensing has been studied intensively. One of the proposed methods for the calibration of such an instrument is the application of a distributed noise injection network. This paper focuses on the origin and effect of errors arising from this methodology. A generalized analytical method to calculate the accumulation of phase and amplitude errors in a distributed noise injection network is presented. This method is then applied to the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS), the interferometric radiometer aboard the European Soil Moisture and Ocean Salinity satellite. The effect of the resulting errors to MIRAS' brightness temperature is analyzed. The presented method is applicable also to other interferometric radiometers, whose calibration relies on distributed noise injection.
IEEE Transactions on Geoscience and Remote Sensing 10/2009; · 2.89 Impact Factor
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ABSTRACT: Interferometric aperture synthesis is a new technology proposed for space-borne remote sensing of sea surface salinity. In the lack of availability of a complete instrument of this kind, validation of the technology for salinity retrieval purposes is desired. In this paper we describe an intense measurement campaign carried out with a complete interferometric aperture synthesis radiometer system HUT-2D. The campaign aimed for the detection of a changing salinity level in the Baltic Sea. We have a special emphasis on the assessment of the impact of sea state on the radiometric measurements, which is considered one of the major obstacles for sea surface salinity retrieval at L-band. For this purpose we study sea roughness information collected with Global Navigation Satellite System Reflectometer.
Geoscience and Remote Sensing Symposium,2009 IEEE International,IGARSS 2009; 08/2009
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ABSTRACT: SMOS is the European Space Agency's next Earth Explorer satellite due
for launch in 2009. It aims for global monitoring of soil moisture and
ocean salinity utilizing a new technology concept for remote sensing:
two-dimensional aperture synthesis radiometry. The payload of SMOS is
Microwave Imaging Radiometer by Aperture Synthesis, or MIRAS. It is a
passive instrument that uses 72 individual L-band receivers for
measuring the brightness temperature of the Earth. From each
acquisition, i.e. integration time or snapshot, MIRAS provides
two-dimensional brightness temperature of the scene in the instrument's
field of view. Thus, consecutive snapshots provide multiangular
measurements of the target once the instrument passes over it. Depending
on the position of the target in instrument's swath, the brightness
temperature of the target at incidence angles from zero up to 50 degrees
can be measured with one overpass. To support the development MIRAS
instrument, its calibration, and soil moisture and sea surface salinity
retrieval algorithm development, Helsinki University of Technology (TKK)
has designed, manufactured and tested a radiometer which operates at
L-band and utilizes the same two-dimensional methodology of
interferometery and aperture synthesis as MIRAS does. This airborne
instrument, called HUT-2D, was designed to be used on board the
University's research aircraft. It provides multiangular measurements of
the target in its field of view, which spans up to 30 degrees off the
boresight of the instrument, which is pointed to the nadir. The number
of independent measurements of each target point depends on the flight
speed and altitude. In addition to the Spanish Airborne MIRAS
demonstrator (AMIRAS), HUT-2D is the only European airborne synthetic
aperture radiometer. This paper presents the datasets and measurement
campaigns, which have been carried out using the HUT-2D radiometer and
are available for the scientific community. In April 2007 HUT-2D
participated in to the first scientific measurement campaign. This
campaign consisted of a single flight over the Gulf of Finland
simultaneously with R/V Aranda's (Finnish Marine Research Institute)
ground truth collection. The vessel measured e.g. sea surface salinity
and sea temperature along the test lines measured with the radiometer
system. During the autumn of 2007 HUT-2D participated in the
CoSMOS-2007 campaign, in which three datasets from the Finnish coastal
area were measured in order to demonstrate sea salinity retrieval. The
campaign consisted of two two-hour measurement flights over an expected
salinity gradient with HUT-2D and the Danish conventional radiometer
EMIRAD. For the reference data, sea surface temperature and salinity
were measured along the gradient line from a vessel. The third flight
included different maneuvers, such as wing-wags, circles, and clover
leafs, over the Gulf of Finland. During the same autumn, HUT-2D was
used to measure datasets in northern Finland for soil moisture retrieval
purposes. The flight consisted of measurement flights over test areas in
Sodankylä, and Pallas. These test sites were equipped with weather
stations of Finnish Meteorological Institute. Also soil moisture samples
were collected at the sites. During the transition flights (approx. 800
km) from southern Finland to these test sites HUT-2D measured
continuously, however, ground reference data for soil moisture was not
collected beyond a few weather stations overpassed. Land classification
maps for the transit flights are available. The most significant
measurement campaign of HUT-2D so far was carried out during the spring
of 2008. This 6-week campaign consisted of measurements of soil moisture
test sites in Germany (Danube Catchment Area, DCA) and Spain (Valencia
Anchor Station, VAS). The campaign at the DCA site consisted of four
two-hour flights over the selected test lines in the Danube river
catchment area, which is actively used for soil moisture studies. The
VAC site consisted of 10 x 10 kilometers area also used for soil
moisture studies. This area was mapped with HUT-2D in four different
days.
03/2009; 11:9575.
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ABSTRACT: An airborne L-band 2-D interferometric radiometer for Soil Moisture and Ocean Salinity (SMOS) measurements has been developed in the Helsinki University of Technology, Laboratory of Space Technology. The first successful flights were conducted in spring 2006. In this paper, the technical description, calibration, and image reconstruction philosophy and the latest results from the use of the instrument are discussed. One of the key goals of the instrument design has been to acquire L-band interferometric data to support the European Space Agency's SMOS mission that employs the L-band interferometric radiometer Microwave Interferometric Radiometer using Aperture Synthesis. Both instruments use aperture synthesis technology for the target image reconstruction in two dimensions.
IEEE Transactions on Geoscience and Remote Sensing 04/2008; · 2.89 Impact Factor
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J. Lemmetyinen,
J. Uusitalo, J. Kainulainen,
K. Rautiainen,
N. Fabritius,
M. Levander,
V. Kangas,
H. Greus,
J. Pihlflyckt,
A. Kontu,
S. Kemppainen,
A. Colliander,
M.T. Hallikainen,
J. Lahtinen
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ABSTRACT: 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.
IEEE Transactions on Geoscience and Remote Sensing 12/2007; · 2.89 Impact Factor
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ABSTRACT: 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 Agency's (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.
Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International; 08/2007
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ABSTRACT: This paper describes a test campaign carried out with synthetic aperture radiometer HUT-2D to establish understanding to the instrument's radiometric performance. The test campaign consists of measurements of the radiation from the sky, which is considered as a well-known target, and measurements of a pure sea water scene, which brightness temperature is possible to model. Results of the tests are used to address instrument's radiometric sensitivity and radiometric resolution. The experimental results are discussed and compared to the theoretical values, where applicable.
Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International; 08/2007
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ABSTRACT: 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 instrument's 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
IEEE Geoscience and Remote Sensing Letters 05/2007; · 1.56 Impact Factor
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ABSTRACT: This paper describes measurements done to verificate and to test the performance of two methods used to calibrate fringe-washing effects occurring with large aperture synthesis radiometers. The methods tested in the paper are the ones proposed for the fringe-washing calibration of the MIRAS instrument of European Space Agency's SMOS mission
IEEE MicroRad, 2006; 02/2006
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ABSTRACT: 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.
IEEE Transactions on Geoscience and Remote Sensing 06/2005; · 2.89 Impact Factor
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ABSTRACT: An L-band airborne radiometer using two-dimensional aperture synthesis (HUT-2D) is under development in Helsinki University of Technology (HUT) for remote sensing. The low measurement frequency is suitable for soil moisture and sea surface salinity measurements. The instrument's technical characteristics are similar to those of the European Space Agency's (ESA) SMOS) (Soil Moisture and Ocean Salinity) satellite instrument in order to support ESA in satellite mission instrument development work. The HUT-2D instrument overview and recent test results are presented in this paper.
Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International; 08/2003
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Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International; 08/2003
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ABSTRACT: The launch of the European Space Agency (ESA)'s Soil Moisture and Ocean Salinity (SMOS) satellite mission in November 2009 opened a new era of global passive monitoring at L-band (1.4-GHz band reserved for radio astronomy). The main objective of the mission is to measure soil moisture and sea surface salinity; the sole payload is the Microwave Imaging Radiometer using Aperture Synthesis. As part of comprehensive calibration and validation activities, several ground-based L-band radiometers, so-called ETH L-Band radiometers for soil moisture research (ELBARA-II), have been deployed. In this paper, we analyze a comprehensive set of measurements from one ELBARA-II deployment site in the northern boreal forest zone. The focus of this paper is in the detection of the evolution of soil frost (a relevant topic, e.g., for the study of carbon and methane cycles at high latitudes). We investigate the effects that soil freeze/thaw processes have on the L-band signature and present a simple modeling approach to analyze the relation between frost depth and the observed brightness temperature. Airborne observations are used to expand the analysis for different land cover types. Finally, the first SMOS observations from the same period are analyzed. Results show that soil freezing and thawing processes have an observable effect on the L-band signature of soil. Furthermore, the presented emission model is able to relate the observed dynamics in brightness temperature to the increase of soil frost.
IEEE Transactions on Geoscience and Remote Sensing · 2.89 Impact Factor
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J. Kainulainen,
K. Rautiainen,
P. Sievinen,
J. Seppänen,
E. Rouhe,
M. Hallikainen,
J. Amico,
F. Schlenz,
A. Loew,
S. Bircher,
C. Montzka
Proceedings of the IGARSS 2010, 702-705 (2010).
