Invited article: Digital beam-forming imaging riometer systems.

The design and operation of a new generation of digital imaging riometer systems developed by Lancaster University are presented. In the heart of the digital imaging riometer is a field-programmable gate array (FPGA), which is used for the digital signal processing and digital beam forming, completely replacing the analog Butler matrices which have been used in previous designs. The reconfigurable nature of the FPGA has been exploited to produce tools for remote system testing and diagnosis which have proven extremely useful for operation in remote locations such as the Arctic and Antarctic. Different FPGA programs enable different instrument configurations, including a 4 × 4 antenna filled array (producing 4 × 4 beams), an 8 × 8 antenna filled array (producing 7 × 7 beams), and a Mills cross system utilizing 63 antennas producing 556 usable beams. The concept of using a Mills cross antenna array for riometry has been successfully demonstrated for the first time. The digital beam forming has been validated by comparing the received signal power from cosmic radio sources with results predicted from the theoretical beam radiation pattern. The performances of four digital imaging riometer systems are compared against each other and a traditional imaging riometer utilizing analog Butler matrices. The comparison shows that digital imaging riometer systems, with independent receivers for each antenna, can obtain much better measurement precision for filled arrays or much higher spatial resolution for the Mills cross configuration when compared to existing imaging riometer systems.

[1]  R. Dicke.  The measurement of thermal radiation at microwave frequencies. , 1946, The Review of scientific instruments.

[2]  B. Burke,et al.  An Introduction to Radio Astronomy , 1996 .

[3]  T. Hagfors,et al.  Performance comparison of cross correlation and filled aperture imaging riometers , 2003 .

[4]  Hisao Yamagishi,et al.  Eastward propagation of PC4‐5 range CNA pulsations in the morning sector observed with scanning narrow beam riometer at L=6.1 , 1988 .

[5]  Farideh Honary,et al.  A Multi-Instrument Data Analysis toolbox , 2004 .

[6]  Mills.  The Distribution of the Discrete Sources of Cosmic Radio Radiation , 1952 .

[7]  R. E. Hibbins,et al.  Utilizing riometry to observe gravity waves in the sunlit mesosphere , 2003 .

[8]  Erling Nielsen,et al.  Plans for a new rio-imager experiment in Northern Scandinavia , 1997 .

[9]  Bahram Honary,et al.  An imaging riometer for ionospheric studies , 1995 .

[10]  Robert J. Mailloux,et al.  Phased Array Antenna Handbook , 1993 .

[11]  Farideh Honary,et al.  On the origin of high m magnetospheric waves , 2010 .

[12]  Farideh Honary,et al.  Time resolution of cosmic noise observations with a correlation experiment , 2004 .

[13]  Yasuhiro Murayama,et al.  Development of a high-resolution imaging riometer for the middle and upper atmosphere observation program at Poker Flat, Alaska , 1997 .

[14]  Farideh Honary,et al.  Comparison of methods to determine auroral ionospheric conductances using ground-based optical and riometer data , 2008 .

[15]  Farideh Honary,et al.  Measurements and modeling of cosmic noise absorption changes due to radio heating of the D region ionosphere , 2011 .

[16]  Farideh Honary,et al.  Triangulating the height of cosmic noise absorption: A method for estimating the characteristic energy of precipitating electrons , 2010 .

[17]  Martin Grill,et al.  Technological advances in imaging riometry , 2007 .

[18]  C. G. Little,et al.  The Riometer-A Device for the Continuous Measurement of Ionospheric Absorption , 1959, Proceedings of the IRE.

[19]  Mills,et al.  A High-resolution Aerial System of a New Type , 1953 .

[20]  S. R. Marple,et al.  High-resolution maps of the characteristic energy of precipitating auroral particles , 2001 .

[21]  Martin Grill,et al.  A flexible streaming software architecture for scientific instruments , 2010, Earth Sci. Informatics.

[22]  D. S. Mathewson,et al.  Scanning the sun with a highly directional array , 1958, Proceedings of the IRE.

[23]  E. Nielsen.  Antenna system for a high resolution imaging riometer , 2001 .

[24]  T. J. Rosenberg,et al.  A phased-array radiowave imager for studies of cosmic noise absorption , 1990 .

[25]  S. R. Marple,et al.  The background absorption at high latitudes , 2003 .

[26]  W. I. Axford,et al.  Small scale auroral absorption events associated with substorms , 1977, Nature.

[27]  M. Beharrell,et al.  A new method for deducing the effective collision frequency profile in the D-region , 2008 .