Martti Toikka

A helicopter-borne eight-channel ranging scatterometer for remote sensing. I. System description

For pt.II see ibid., vol.31, no.1, p.170-9 (1993). HUTSCAT, a helicopter-borne dual-frequency FM-CW scatterometer, is described. The HUTSCAT measures the backscattering properties of a target with a range resolution of 65 cm. The real-time ranging capability is obtained by performing the fast Fourier transform (FFT) to the received time-domain signal. The measurement is made simultaneously at eight channels (VV, HH, HV, and VH modes of polarization at 5.4 GHz and 9.8 GHz). The scatterometer measures the radar return spectrum for eight channels in 16.6 ms, which corresponds to an along-track distance of 0.33 m for the helicopter speed of 20 m/s. The radar system has been designed for remote sensing of forests, sea ice, and snow. >

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.

Helicopter-borne measurements of radar backscatter from forests.

Abstract Helicopter-borne scatterometer measurements of various forest and surface types were conducted in spring 1988 in Espoo, near Helsinki. The scatterometer operates at 5-4 and 98 GHz and employs four linear polarizations (VV, HH, VH and HV). At each of the eight channels the radar can measure the backscattering properties of a target with a range resolution of 1 metre. The experimental results indicate that the location of backscattering sources within the forest canopy varies substantially with tree species. By applying principal-component analysis to the radar return versus range spectrum, identification of tree species is shown to be possible.

Microwave Dielectric Properties Of Low-salinity Sea Ice

A waveguide transmission system was used to measurt the dielectric properties of sea ice during the BEPERS-87 (Bothnian Experiment in Preparation for ERS-1) Campaign in the Gulf of Bothnia, March 31 April 3, 1987. The temperature range of the icb samples was -6.0 to -0.3OC and the salinity range

Classification of Sea Ice Types with Radar

Using a helicopter-borne multichannel scatterometer (accurately calibrated non-imaging radar), the feasibility of using synthetic aperture radar (SAR) images from present and near-future spaceborne sensors for assisting winter navigation in the Baltic Sea was investigated. Due to cloud cover and short days in the winter, visible/infrared satellite data cannot be used for Baltic ice mapping. In order to decrease the operating cost of icebreakers, real-time radar-derived sea ice charts are needed to optimize the route selection of icebreakers assisting ships to Finnish and Swedish harbors. For ship navigation, information on (1) new ice and open water (preferred route), (2) level ice (second choice) and (3) ice ridges and rubble fields (should be avoided; may stop an icebreaker) is of primary importance. Four helicopter-borne radar campaigns were organized in 1988-1992 in order to experimentally study the radar response to different Baltic ice types. Measurements for six ice categories and open water were conducted under various weather conditions (wet and dry ice and snow surfaces). Based on the experimental data set, (1) the optimum radar parameters for Baltic ice mapping were determined, followed by three additional recommended systems, and (2) the feasibility of using synthetic aperture radar (SAR) images from present (ESA ERS-1 satellite) and near-future (ESA ERS-2 satellite, U.S. SIR-C Shuttle mission and Canadian Radarsat satellite) missions for discriminating sea ice categories was evaluated.

Scatterometer measurements of Arctic sea ice at C-band

The Arctic-91 expedition was a part of a project for calibration and validation of the ERS-1 Synthetic Aperture Radar, and for studying its feasibility for sea ice mapping. The authors MINISCAT scatterometer operating at the ERS-1 SAR center frequency of 5.3 GHz was used for the airborne measurements. Targets measured with MINISCAT consisted of four different ice types with ice thickness varying from 5 cm to more than 3 metres. The temperature during the mission varied from +2/spl deg/C to -16/spl deg/C. The results show that W and VH polarizations together can be used for ice type discrimination, but single-polarization measurements alone do not provide a reliable discrimination. No significant temperature correlation could be found in the case of dry snow cover.<<ETX>>

Backscatter Behaviour Of Low-salinity Sea Ice At C- And X-band

A helicopter-borne dual-frequency scatterometer was used to investigate the backscattering behavior of low-salinity sea ice at 5.4 GHz and 9.8 GHz. The measurements were conducted in the BEPERS-88 Sea Ice Campaign in the Gulf of Bothnia, March 6-12, 1988. The backscattering properties of several sea ice types were examined at the two frequencies, using HH, VV, HV, and VH polarization modes.

Radar Backscatter Signatures of Baltic Sea Ice

A helicopter-borne 8-channel scatterometer (5.4/9.8 GHz; VV, HH, VH, HV polarizations) was used to investigate the backscattering behavior( of low-salinity sea ice in the Gulf of Bothnia. The radar response to several ice types was measured using three different incidence angles under cold winter conditions (air temperature -15°C to -20°C). The goal of the project is to (a) evaluate the feasibility of ERS-1 SAR for ice type classification and (b) to determine the optimum radar parameters (frequency, polarization, incidence angle) for remote sensing of low-salinity sea ice.

Microwave Radiometer And Radar Measurements In The SAAMEX Campaign

The Surface and Atmospheric Airborne Microwave Experiment (SAAMEX) was held in Finland on 14-21 March 1990. The institutes providing airborne microwave sensors for the campaign were the British Meteorological Office (BMO) and the Helsinki University of Technology (HUT). The three main targets were sea ice, snow, and forest canopies. Ground truth measurements were made by several Finnish research institutes.

Development Of Airborne Dual-frequency Scatterometer

A he1 icopter-borne dual -frequency FM-CW scatterometer for remote sensing is described. The scatterometer can measure the radar b ackscatter from a target w ith a range resolution of one meter. The measurement is made simultaneously at eight channels (VV, HH, HV, and VH modes of polarization at 5.4 GHz and 9.8 GHz). 1. SUMMARY