Anssi Hakkarainen

Radiometric Performance of the SMOS Reference Radiometers—Assessment After One Year of Operation

In this paper, we present an analysis of the radiometric performance of the three 1.4-GHz noise injection radiometers of the European Space Agencys Soil Moisture and Ocean Salinity (SMOS) satellite. The units measure the antenna temperature, which contributes to the average brightness temperature level of SMOS retrievals. We assess the radiometric resolution of the receivers, the similarity between their measurements, and their thermal stability. For these purposes, we use SMOS measurement data gathered during the first year of the orbital operations of the satellite, which was launched in November 2009. The main results from the analysis are that the units meet the design requirements with a margin. Also, we present a new thermal model for the radiometers to further enhance their stability.

Studies of radio frequency interference at L-band using an airborne 2-D interferometric radiometer

Potential radio frequency interference (RFI) sources at L-band include L-band radars; mobile, navigation and other satellite services; and various land services. We have collected data using our airborne L-band interferometric HUT-2D radiometer in order to support the ESA SMOS mission. We participated in April-May 2008 in ESAs rehearsal campaign for SMOS satellite validation activities in Germany and Spain. Additional data have been collected in Finland. Two basic categories of RFI have been observed: (1) Point-wise weak sources that do not saturate the HUT-2D instrument, and (2) strong sources that totally saturate the sensor over a large area.

Aalto-1: a hyperspectral Earth observing nanosatellite

This paper introduces the Aalto-1 remote sensing nanosatellite, which is being built under the coordination of The Department of Radio Science and Engineering of Aalto University School of Electrical Engineering. The satellite is a three unit CubeSat, and it will be mostly built by students. The satellite platform is designed to house several payloads, and the main payload of the Aalto-1 mission will be the worlds smallest hyperspectral imager while secondary payloads being a compact radiation monitor and an electrostatic plasma brake for de-orbiting.

Brightness temperature behavior of snow on lake ice over a wide frequency range

We have conducted airborne microwave radiometer campaigns over a test site consisting of two lakes and their immediate surroundings in Southern Finland since 2004 in order to (1) determine the effect of snow cover to the brightness temperature of lake ice, and to (2) compare the brightness temperatures for snow-covered lake ice and snow-covered terrain (both open and forested areas). Measurements have been conducted under a variety of weather and snow/ice conditions covering situations from early winter to melting season. Using the HUTRAD and HUT-2D radiometer systems a frequency range of 1.4 to 36.5 GHz is covered. Airborne measurements are always accompanied with in-situ data collection including relevant snow, ice, and terrain parameters.

Investigation of Radio Frequency Interference at L-band using data from airborne HUT-2D radiometer and spaceborne SMOS radiometer

The launch of the European Space Agencys (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 Earths 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.

Measurements and Simulation of a Concentric Raised Bog with a 1.4-GHz Radiometer

A concentric raised bog is a common mire type in the southern boreal zone. The mires play an important role in the hydrological cycle of the environment, as their moisture is usually significantly different from open agricultural land or forest. The hydrological parameters, such as soil moisture (SM), are increasingly assessed by means of remote sensing. However, the microwave radiation properties of bogs have not been widely studied in the scope of L-band radiometry, an important technology for SM observations. In order to address this topic, this letter presents an analysis of measurements of a concentric open bog with a 1.4-GHz airborne radiometer. The series of airborne measurements are collected, along with ground measurements, in southern Finland. A two-layer emission model is used to simulate microwave emission of the bog in different moisture conditions. Results show that 1.4-GHz radiometry is sensitive to bog surface conditions, such as changes in moisture content and distribution. We also show that despite the significant difference in soil moisture, the bog has emissivity characteristics more similar to agricultural rather than forested area.