Tuomo Auer

Helsinki University of Technology L-Band Airborne Synthetic Aperture Radiometer

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 Agencys 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.

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.

Development of airborne aperture synthetic radiometer (HUT-2D)

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 instruments technical characteristics are similar to those of the European Space Agencys (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.

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.

Thermal stabilized front-end PCB with active cold calibration load for L-band radiometer

In this paper, the thermally stabilized front-end of an L-band total power receiver is presented. Applications on the L-band have become one of the most important focus points in the field of passive microwave remote sensing. Measuring environmental parameters such as ocean salinity and soil moisture remain a challenge, posing strict requirements to instrument performance. For traditional radiometers, especially the stability of front-end components is critical. The principle of the stabilization technique and the actual design are described. The design also features an on-board active cold load for calibration purposes. The presented technique aims to stabilize the front-end section PCB with heaters to sub 0.05 C level.

Advanced airplane version of the HUT 93 GHz imaging radiometer

The HUT 93 GHz Airborne Imaging Radiometer (AIR-93) is being modified in an advanced airplane version. The new features include: a) the use of an attitude-dGPS instrument to produce gyro data for radiometer beam active stabilization, b) an improved version of the airborne, liquid nitrogen cooled cold calibration target, and c) the digital, computationally stabilized, position oriented optical comparison image system.

The first results of a novel 93 GHz airborne imaging radiometer

A 93 GHz conically scanning dual-channel (H&V) imaging radiometer has been built at the Helsinki university of Technology (HUT). The system has been designed for the Bell Jetranger helicopter, but can also be installed aboard the HUT remote sensing aircraft. The new features of the compact instrument are its ability to follow any feasible conical scan path, the airborne liquid nitrogen cooled cold calibration load as well as a flat panel color display providing a real-time false colour image and video image window. The very first experiences of the instrument are promising, and some of the data measured so far are presented.

Development and characterization of fully polarimetric noise injection radiometer for MIRAS

An L-band noise injection radiometer (NIR) has been designed and implemented by Helsinki University ofTech- nology Laboratory ofSpace Technology f or the SMOS (Soil Moisture and Ocean Salinity) mission ofESA (1). The work is performed as a part of ESAs MIRAS Demonstrator Pilot Project-2 (MDPP-2) under a subcontract for EADS-CASA. Other partners in the MDPP-2 NIR project are Toikka Engineering Ltd. and Ylinen Electronics Ltd. NIR will work as a part ofthe MIRAS (Microwave Imaging Radiometer Using Aperture Synthesis) instrument. Its main purpose is (1) to provide precise measurement ofthe average brightness temperature scene for absolute calibration of the MIRAS image map and (2) to measure the noise temperature level ofthe internal active calibration source f or individual receiver calibration. The performance of NIR is a decisive factor ofthe MIRAS perf ormance. The challenge in the implemented, so-called blind correlation, method is the fact that there is additional noise in the correlated signal due to using the noise injection method. The main objective ofthis paper is to demonstrate the f ofthis technique. I. INTRODUCTION The precision of a noise injection radiometer is based on comparing the measured signal to two reference sources, the noise temperatures of which are known. This will remove the effect of the receiver gain and offset variations. The length of the noise pulse is then proportional to the antenna temperature (2). NIR will also be used in the MIRAS array as a regular receiver unit for interferometric image creation. In addition to measuring the horizontally and vertically polarized antenna noise temperature and the calibration net- work noise temperature, the MDPP-2 NIR was designed to provide fully polarimetric measurement capability. The Stokes parameters are retrieved using the same correlator, which the MIRAS uses for solving the correlation for the interferometric image creation. The so-called modified Stokes parameters are defined under the Rayleigh-Jeans approximation as (3)