# Crowded Space: A Review on Radar Measurements for Space Debris Monitoring and Tracking
## 4 European Countries' Radar Measurements
The blind zones at various LEO altitudes correspond to areas where at least some part of the returning echo was blocked due to the pointing geometry  
Figure 16: Time–altitude distribution of events at the beginning (**a**) and end (**b**) of the International Polar Year (IPY) campaign performed by the EISCAT Svalbard Radar (ESR) [34]. Reproduced with permission from [PERSON], EISCAT Space Debris During the IPY—A 5000 Hour Campaign; 5 th ESA Space Debris Conference, Darmstadt, Germany, 30 March-2 April 2009.  
of the radar. Both campaigns' results show interesting peaks of detection at 1000 and 1500 km altitudes. Figure 17: Summary plots of the Manda campaigns: range vs. effective diameter and altitude vs. event count for 11–13 August 2005 (**a**,**b**), and 17–20 November (**c**,**d**) [35]. Reproduced with permission from [PERSON], Small-Size Space Debris Data Collection with EISCAT Radar Facilities; Final Report of ESOC Contract 18575/04, 2006. Figure 18: Summary plot of the Cp2 campaign (7–29 September 2005) for 4 different antenna positions: altitude vs. effective event rate (**a**) and range vs. effective diameter (**b**) [35]. Reproduced with permission from [PERSON], Small-Size Space Debris Data Collection with EISCAT Radar Facilities; Final Report of ESOC Contract 18575/04, 2006. Actually, the EISCAT UHF radar was also recently employed in its tristatic configuration. The tristatic radar was used for a brief 15 h campaign on 25 May 2010, detecting 14 events [36]. The raw sample data were recorded from the three receiving sites in Tromso, Kiruna, and Sodankyla. For this particular space debris measurement, the tau1 transmission was employed, which consists of alternating codes spaced by 1160 \(\upmu\)s with duty cycle equal to 8.6%. The operating frequency transmission was 930 MHz, the peak power 2 MW, and the measurement was performed in beam-park mode [36]. The RCS of the detected objects is reported in Figure 19 and compared with the results predicted by the US satellite catalog. An important binomial in European radar debris measurements is the TIRA-Effelsberg bistatic system. The Research Establishment for Applied Science (FGAN) Tracking and Imaging Radar (TIRA) is a 34 m fully computer controlled parabolic antenna with Cassegrain optics located in Wachtberg, Germany. It can operate both in L-band (1.33 GHz) as a narrow-band monopulse tracking radar and Ku-band (16.7 GHz) as a high range resolution imaging radar [37; 38]. The L-band transmitter of the TIRA is able to generate high frequency pulses, typically from 1 to 2 MW peak power, in Right-Handed Circular Polarization (RHCP) [37; 38]. Used as a monostatic radar, the TIRA is capable of detecting 2 cm-sized objects at 1000 km range. However, when combined with the Max-Planck-Institute of Radio Astronomy (MPIfR) Effelsberg radio telescope, a 100 m diameter parabolic dish located in Bad Munstereifel (Germany), as a receiver, the size of detectable objects reaches 0.9 cm. By virtue of a contract with ESA/European Space Operation Center (ESOC), TIRA was employed for three beam-park experiments in 1993, 1994, and 1996. On all three occasions, the radar was operating in monostatic configuration. However, in 1996, a second data collection was recorded at Effelsberg. This last campaign is known as Cooperative Beam-Park Mode 1996 (COBEAM-1/96) or, simply, the COBEAM experiment. It was a 24 h campaign undertaken on 25 November 1996, with an overall number of detections equal to 499 [38]. The experiment was focused on covering a region of the space which was believed to be populated by NaK droplets leaking from the reactor of the Russian satellite RORSAT. The debris detection rate vs. altitude is reported in Figure 20a, for the TIRA in monostatic configuration and with the Effelsberg radio telescope as a receiver, showing that in the 750-1050 km altitude interval the detection rate of the bistatic configuration is much higher. Figure 20b shows the complete data set with the altitude as a function of the Doppler inclination.