Bistatic Space Borne Radar for Early Warning

Transcription

1 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning G. Picadi, A. Masdea STS Via Robecchi Bichetti, Roma ITALY Phone: , Fax: L. Tofone MoD Italy, Teledife, II Repato, V Divisione Viale dell Univesità, Roma ITALY Phone: , Fax: luigi_tofone@hotmail.it L. Bogaelli, L. Ceeoli Alenia Spazio S.p.A. Via Saccomuo, Roma ITALY Phone: , Fax: leonado.bogaelli@aleniaspazio.it ABSTRACT The Bistatic Rada achitectue, with ealy waning capability, has been analyzed consideing the Tactical Ballistic Missiles (TBM), cuise missile and aicaft, as pefeed theats. This study is addessed to analyze the equiements and a pope design of a space bone Bistatic SAR (BSAR) with the elevant pefomance. The bistatic solution has been consideed as a pefeed one due to the good immunity to potential jamme pesent on the theate aea, allowing also a educed value of peak tansmitte powe, pemitting to utilize quite all the tempoal inteval fo the signal tansmission without inteuption duing the eceiving phase. The BSAR technique pemits to incease the esolution in ode disciminate closely tagets. In addition this pape investigates the imaging of an isolated fast moving pointing object (MPO) and the clutte cancellation needed in pesence of fixed teain/sea backgound (featue expected in the ealistic situation of an object moving ove a teain o ove the ocean). 1. INTRODUCTION In view of this gowing potential theats to Euope this study is addessed to analyze the system achitectue and the ada chaacteistics that can give an ealy waning capability fo a suitable immediate defense eaction. In paticula this study addesses the poblem of equiements desciption and design of a space bone bistatic SAR. The tansmitte will be on boad one o moe geo-stationay o HEO satellites while the eceive only on boad the LEO satellite constellation. In this solution the LEO satellite constellation will be simple and lighte due to the absence of the tansmitte on boad each LEO satellite. The dawbacks, on this solution, ae the ange between the tansmitte and the illuminated taget, the lowe eliability in case of a tansmitte failue. The BSAR equies synchonization between the tansmitte satellite and the Picadi, G.; Masdea, A.; Tofone, L.; Bogaelli, L.; Ceeoli, L. (005) Bistatic Space Bone Rada fo Ealy Waning. In Integation of Space-Based Assets within Full Spectum Opeations (pp ). Meeting Poceedings RTO-MP-SCI-150, Pape 17. Neuilly-su-Seine, Fance: RTO. Available fom: RTO-MP-SCI UNCLASSIFIED/UNLIMITED

2 Repot Documentation Page Fom Appoved OMB No Public epoting buden fo the collection of infomation is estimated to aveage 1 hou pe esponse, including the time fo eviewing instuctions, seaching existing data souces, gatheing and maintaining the data needed, and completing and eviewing the collection of infomation. Send comments egading this buden estimate o any othe aspect of this collection of infomation, including suggestions fo educing this buden, to Washington Headquates Sevices, Diectoate fo Infomation Opeations and Repots, 115 Jeffeson Davis Highway, Suite 104, Alington VA Respondents should be awae that notwithstanding any othe povision of law, no peson shall be subject to a penalty fo failing to comply with a collection of infomation if it does not display a cuently valid OMB contol numbe. 1. REPORT DATE 01 AUG 006. REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE Bistatic Space Bone Rada fo Ealy Waning 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) STS Via Robecchi Bichetti, Roma ITALY 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR S ACRONYM(S) 1. DISTRIBUTION/AVAILABILITY STATEMENT Appoved fo public elease, distibution unlimited 11. SPONSOR/MONITOR S REPORT NUMBER(S) 13. SUPPLEMENTARY NOTES See also ADM0138, Integation of Space-Based Assets within Full Spectum Opeations (Integation des moyens spatiaux dans toute la gamme des opeations., The oiginal document contains colo images. 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified 18. NUMBER OF PAGES 3 19a. NAME OF RESPONSIBLE PERSON Standad Fom 98 (Rev. 8-98) Pescibed by ANSI Std Z39-18

3 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning eceives on boad the LEO satellite constellation. Theefoe a diect communication link between the tansmitte and the eceive is necessay in ode to measue the fequency and the phase of the eceived signal efeed to the tansmitted signal. The imaging of an isolated moving point like object and the clutte cancellation technique ae analyzed consideing the ealistic situation of a taget moving ove a teain o ove an ocean aea.. SYSTEM REQUIREMENTS The wide aea coveage has an extension of about 00 km 9400 km. Within this aea coveage ae defined the theate egions (access aea) that will have an extension of about 1500 km 1500 km. An a pioi knowledge of which theate aea has to be coveed will pemit to concentate the suveillance of the satellite constellation only on this specific aea. Afte detection and tack extaction of a theat within the theate aea the system must be capable to maintain the tack of the detected taget as well to maintain the suveillance task on the assigned cisis aea. The system availability equied is 80 % with a econfiguation capability (fo a new cisis aea) within 4 hous. The theats to be detected and engaged ae: TBM; Cuise missile; Aicaft. The missile and aicaft theats have been defined in tems of ada paametes, in ode to select the best ada solution fo the satisfaction of the equiements as follows: Taget RCS 0. m. The Rada Coss Section will fluctuate accoding to Sweling case 1; Altitude within 50 Km- 400 Km fo TBM, 00 m- 400 m fo cuise missile and 00 m-10 Km fo aicaft; Maximum ange fo TBM 3500 km. Time of flight fo TBM 1 15 minutes.aveage absolute velocity fo TBM.5 km/sec.; Delivey to gound based ada of the taget position within a basket of km. Fo tacking equiements (plot association, tack fomation) the esolution will be within 1 km; Pesence of jamming on boad and on gound enemy ada; Gound/Sea clutte level to be consideed. Two configuations have been peliminay consideed and envisaged as potential candidates fo a design base: Tansmitte on boad geo-stationay satellite and eceive only on boad the satellite constellation; Tansmitte and eceive on boad each satellite on the constellation. As stated in the intoduction the fist solution (bistatic) has been selected as a pefeed one consideing that also if the second solution has the advantage to be moe eliable (e.g. if one TX fails the mission is not completely jeopadized) thee is a dawback in tems of cost due to the tansmitte on boad each satellite. The constaint on the system configuation (ada and satellite constellation) is the minimization of the numbe of satellite (fo a ealistic and feasible design). They should be as low as possible (e.g. less than 100 satellites should be a goal) fo the eduction of cost, maximization of utilization with affodable management and maintenance. This constaint, consideing the theate aea of 1500 km 1500 km (vey wide swath capability), has suggested the utilization of the following techniques: 17 - RTO-MP-SCI-150 UNCLASSIFIED/UNLIMITED

4 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning Use of lage antennas; Beam foming and phased aay; SCANSAR. Moeove we can notice that: The eason fo the selection of the bistatic SCANSAR solution is a good tade-off between numbe of satellites needed and the LEO constellation lightness including sola aays due to the tansmitte absence. It has to be consideed that a sophistication fo the tansmittes on HEO is, in any case, unavoidable. In addition the bistatic geomety pemits to utilize all the tempoal inteval fo the tansmitte without inteuption duing the eceiving phase. It is possible to utilize CW signal (coded) with lowe peak powe and highe adiometic pefomance; The Signal to Noise atio (SNR) is a citical paamete, consideing the satellites geomety (ange) and the limited value of the ada coss section of the tagets. In addition the SNR is stongly coelated with the powe density on the taget and theefoe to the swath dimension (TX and RX antennas gain); The theate aea (swath size) is too much extended to be coveed with a easonable numbe of satellites; The esolution equiements, fo the taget spatial identification, ae in good ageement with the beam dimension duing acquisition and also duing tacking, due to the impovement facto, elated to the implementation of the Synthetic Apetue concept (SAR), taking into account the integation of a cetain numbe of pulses (defined by the time needed to geneate the synthetic antenna efeed to the p..f.). In ode to aive to a feasible solution, few constaints have been assumed, consideing the pesent and futue (next 10 yeas) state of the at technology: The maximum available tansmitte powe can not be geate than 75 KW fo pactical easons; The antenna dimension has been limited to 15 m 15 m (limited to these values by mechanical poblems); A fequency utilization within the L band (1 GHz) has been selected as a good tade-off between loss and components availability (antenna and tansmitte). 3. BISTATIC GEOMETRY In ode to analyze the constaint elated to the Range esolution a paticula bistatic intecept geomety is shown in figue 1. RTO-MP-SCI UNCLASSIFIED/UNLIMITED

5 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning z v Tx TX v Rx α t α RX α α R 10 R 31 R 11 h t h R 30 α α P y x Figue 1 The satellite tajectoies must be compensated in ode to pefom the synthetic apetue. The elation that consides the value of R 30 in figue 1 must be modified when consideing the adial component of the velocity. In ode to choose the ight cente of the swath, along the y axis, we can define the bistatic ellipse as the collection of points P so that the sum TP + PR is constant (whee TP is the tansmitte-point distance and PR is the point-eceive distance). If we conside two consecutive ellipses which coss the y axis in P1 and P espectively the diffeence δ = ( TP + P R) ( TP1 + P1 R) epesents the bistatic ange cell esolution in the slant plane. This distance, consideed in the gound plane (x, y plane), is the distance between the two consecutive ellipses. Theefoe, if P 1 is placed in (0,y 1,0), P will be in (0,y 1 +R D,0) whee R D is the ange esolution. Moeove δ is connected to the tansmitted chip bandwidth B by the elation c δ =. We can calculate, afte having imposed the ange esolution R D, the chip bandwidth B as a B function of the coodinate y 1 fo the cente of the swath. The figue shows that, if we impose, fo example, a ange esolution of 500 m and a swath centeed in y=700 Km, we need a chip bandwidth of about 1. MHz RTO-MP-SCI-150 UNCLASSIFIED/UNLIMITED

6 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning Figue In ode to evaluate the Dopple chip we can wite the fequency slope as [3]: whee: PR df dt The azimuth esolution is equal to: and the integation gain is given by: B A = T A T A h cosα λ PR 0 = (1) L V [ h tgα + y] + h + + sin α RX cos h 3 = PR = y 0 t= 0 x= 0 T whee α is shown in figue 1. In ode to avoid aliasing poblem it is necessay that: A RX R V V L y RX RX AZ = (3) BA VRT λ h λ VRT h = BATA (4) L V cosα L V cosα p P df V RX α P RT.. f. > BA = TA (5) dt L We can notice that the last appoximations can be accepted in case of slow taget motion. () 4. TARGET ENGAGEMENT The acquisition phase is a continuous pocess (multiple taget detection equiement) while the tacking pocess will stat, afte the detection, fo each taget. RTO-MP-SCI UNCLASSIFIED/UNLIMITED

7 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning The signal to noise atio fo bistatic ada, afte compession gain, can be witten as: P SNR = p σ τ At A 4πλ Rt R KTFL whee: A t, A ae the tansmitte and eceive antenna aea, λ is the wavelength of the tansmitted fequency, R t, R ae the ange tansmitte-taget and eceive-taget, σ is the taget ada coss section, KTBF is the noise powe and L is the system loss. In ode to obtain at least an SNR value of 1 db, by the pevious equation, we can calculate the pulse duation as shown in table 1. (6) Table 1 f = GHz Paamete Value db Note Pp 75 kwatt λ (0.15) Wavelength K Boltzman constant T 300 K 4.7 Tempeatue K At A (15 15) m4-47 Tansmitte antenna aea F L 3 Noise figue and loss 4π Σ 0. m 6.98 Bistatic ada coss section R=( h/cosα) (1830) Km 15. Rt=( ht/cosαt) (4315) Km 13.7 R = h/cosα Rt = ht/cosαt SNR 1 Τ 3 ms 5 >vt τ > 7.5 m Range esolution It has to be consideed that this gound esolution is enough fo the detection (the equiement is a basket of km). The IF (impovement facto) fo the clutte cancelle has to educe the clutte below the noise level and, at least, a double cancelle is needed. An altenative solution is to limit the scanning to a sufaces that ae positioned at a suitable height with efeence to the gound sufaces. Concening the Tacking phase, we can notice that an advantage to use the SAR is the possibility to detect closely taget within the equied basket RTO-MP-SCI-150 UNCLASSIFIED/UNLIMITED

8 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning It is staightfowad to conclude that the SAR technique poduces a bette on gound esolution and theefoe educes the needed clutte cancellation (impovement facto). The CSR (Clutte to Signal Ratio) consideing a locally homogeneous teain is equal to: 0 σ δ δ az CSR = (7) σ whee δ and δ az ae espectively the ange and azimuth esolution on the gound while σ0 (assumed equal to 0.01 fo typical scenaio) and σ ae espectively the on gound backscatteing coefficient and the taget coss section. Assuming the possibility to each a value of CSR equal to -0 db, by having a ange and azimuth δ and δaz,we can find out the necessay Impovement Facto(IF), as shown in Fig. 3. Figue 3 It is evident, by the figue, the esolution equied in ode to obtain a feasible IF. The design of the system is pefomed in ode to initialize the tacking only on the detected tagets duing the acquisition phase. In this way the system is opeating simultaneously a continuous seach and a tacking. The tacking pocess can be impoved by the utilization of the SCANSAR technique. In this way it is possible to tack the taget, also in pesence of an heavy fading, once an estimation of the taget tajectoy has been obtained by the detection pocess. Moeove by geometic manipulations we obtain [3]: L V RT > SR = ymax ymin R = ymax ymin S R cos 3 α γ Hc (8) λ h h R = b λ = (9) b cos α cos α R By the equation (8) appeas that swath dimension S R and esolution R ae stictly elated and in ode to incease the dimension of the swath a lage dimension of physical antenna is equied; the limitation on swath dimension is a majo poblem consideing the equied lage dimension of the coveage aea. The dimension of the eal antenna imposes constaints on swath dimension and its maximum pemissible dimensions longitudinal (coss tack) and tansvesal (along tack) must satisfy the eq.s (8) and (9). In ode to cove an access aea of 1500*1500 Km the SCANSAR technique divides the whole aea in a RTO-MP-SCI UNCLASSIFIED/UNLIMITED

9 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning numbe of sub-swaths N *N c. The constaint that the access aea A q will be completely coveed duing the satellite tajectoy is defined by: ( 1500) Km T N N 1500 Km / V = 00sec A (10) q = A c RX whee N and N c ae the numbe of vetical and hoizontal sub-swaths necessay to cove the access aea (see Fig.4) and T A is the acquisition time necessay to obtain a SAR image of one sub-swath Km N 1500 Km N c Figue 4 To evaluate T A we have to conside that the maximum time available in ode to avoid the taget migation outside the SAR esolution cell, within two pulse epetition inteval (minimum condition necessay to pefom a suitable clutte cancellation), is equal to: T R AZ a = (11) vt whee v T is the taget velocity. T a is the maximum time available to obtain the SAR image. The SAR esolution is given by: V V R = L RX RX AZ = (1) BA VRT whee V RX is the eceive velocity and B A is the Dopple chip bandwidth defined by equation (5). The time necessay to obtain the SAR synthetic apetue is equal to: λ h 1 T A = (13) L cos αp VRX 17-8 RTO-MP-SCI-150 UNCLASSIFIED/UNLIMITED

10 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning Imposing T = T we obtain the eal antenna dimension: a R v AZ T A VRX λ h 1 λ h L V v ( 430) = L = RT T m L 430m v V L cosα V = (14) V cosα T RT whee V RT is the LEO satellite velocity equal to 7.6 Km/s. P RX RX This states that it s impossible to pefom an usual SAR pocessing which use the whole synthetic apetue. So we have to use a synthetic sub-apetue which is a faction (equal to1/nl) of the maximum pemitted synthetic apetue length and follows that: V V R = The equation (13), consideing the equation (16) becomes: T P RX RX AZ = N L L N L (15) BA VRT T A λ h 1 = (16) NL L NL cos αp VRX TA ( ) λ h V v ( 430) = L NL = RT T m L NL 430 m N = (17) V cos α a = L RX P In this way the numbe of sub-apetue N L in which the synthetic antenna is divided can be chosen so that we can obtain a feasible antenna dimension L. Theefoe the maximum pemissible value of the azimuth esolution is: VRX RAZ = L N L 45m (18) V In this case the synthetic sub-apetue is equal to: RT λ h Ls = 640 m (19) L N cos α L With the assumption in (17) the value of T a becomes: TA RAZ Ta = = N v = s (0) L The numbe of sub-swaths is given by: 00sec T a N N c 00sec N N c 353 (1) T The tansmitte swath must be geate than eceive swath fo pactical easons and to veify this condition, as an example, the maximum possible value fo antenna dimension ae: t λ ht A t = = 5m S p = Km () At cos αpt T P a RTO-MP-SCI UNCLASSIFIED/UNLIMITED

11 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning In ode to satisfy the above constaint A = Lb 10m, we can choose, in ode to obtain a appoximately squae swath, L =11 m, b =11 m, then N L is: L N 430 m N 39 (3) L = L So we can conside only 1/39 of the whole synthetic apetue. With this value we obtain the stated esolution of 45 m. The azimuth compession gain is defined as the numbe of pulses integated in the acquisition time TA T a = and then it can be witten as p.. f. Ta. N L The clutte equiements imposes to maintain the swath as small as possible. The time equied to cove the access aea is 00 sec, and potential tagets launched duing the acquisition and tacking time can not be detected unless seveal LEO ae utilized. In ode to ovecome this poblem, if a peliminay infomation, on possible launch sites, is available, the acquisition and tacking can be focused only on these sites. In this case the coveage pecentage can be inceased and simultaneously will also incease the pobability to discove simultaneous theats, diffeently located, in the access ae. 5. CLUTTER EVALUATION If we accept to detect the theat at a cetain altitude we can conside that the tansmitte and the eceive ae not pointed on the gound but at a paticula height. Theefoe the swaths on the gound ae not in the same location and then the influence of the clutte could be educed (if the two swaths ae not ovelapped, the clutte will be absent, at least in the main lobe) (see Fig.5). z TX α RX α Pt α α P h t h h tag y t 700 Km y y x Figue RTO-MP-SCI-150 UNCLASSIFIED/UNLIMITED

12 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning In ode to avoid the clutte in the main lobe of the eceive we have to point the antennas at a highe altitude. It has to be highlighted that to avoid the constaint that the taget will be detected only at vey high height we can educe the eceive swath inceasing the eceive antenna aea up to 5 m (pesently has been fixed at 10m ). This constains can only be emoved if we educe the access aea. When utilizing clutte cancelle the Moving Point Object (MPO) detection and velocity estimation can be pefomed eithe incoheently, with a single SAR apetue, o coheently, with two o moe apetues [0]. If the eceive antenna is patitioned in two apetues along tack diection, coheent pocessing can be used to find moving objects and estimate thei velocities. The fundamental pinciple is that each apetue (phase cente) obseves the scene fom the same point in space at a diffeent time. Featues whose ange location has shifted fom one scene to the next ae movingtaget candidates. SAR data fom each apetue ae focused to a complex image and the image content is common except fo scene changes ove time τ. Fo land scenes fixed elements ae stationay ove time τ and thei images will be vey nealy identical. Moving objects will be displaced between the two scenes, and these displacements can be measued as phase shifts: Displaced Phase Cente Antenna (DPCA). The SAR DPCA analysis is made by the coelation between the complex sample sets of the fist apetue image, S 1, and the second apetue image, S, to yield: J = S 1 S = S jφ1 jφ ( e e ) φ 1 + φ π φ j + 1 J = S 1 sin (3) φ The magnitude of the subtacted DPCA signals is a sinusoidal function, whose agument is diectly popotional to the speed v tag of the scene elements. Tansfe function of the DPCA cancelle is given by []: e H ' η f f d θ = 1 + tan sin π (4) f ( f, ) The pefomance of the moving taget indication with DPCA ae shown in []. 6. CONCLUSIONS The satisfaction of the main equiements can be obtained with a Bistatic configuation utilizing the phase aay technology. The use of BSAR pemits to incease the esolution and disciminate closely tagets. The peliminay study shows that the bistatic solution is a good tade off fo the feasibility of the system. The availability of the satellites on the theate is a function of the numbe of satellite within the LEO and HEO/GEO constellation. The tansmitted powe needs to be vey high, fo the given SNR (low taget RCS), and its value can be obtained by summing the powe of moe than one HEO satellite. The obit selection, when opeating with BSAR must be selected accuately in ode to intecept the taget accoding to the necessay geomety. RTO-MP-SCI UNCLASSIFIED/UNLIMITED

13 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning REFERENCES [1] G. Picadi et alii "Bistatic Model of Ocean Scatteing " IEEE T. Antennas Popag. Vol. 46 n.1oct.98 [] A. Ciaffone et alii " Application of the Pais concept to the GPS Signals " T.R. n [3] A.K.Fung and H.J.Eom, "Coheent Scatteing of a Spheical Wave fom an Iegula Suface IEEE T. Antennas Popagat. Vol. AP-31, pp. 68-7, Jan [4] B.Levine, "Fondaments Theoiques de la Radiotechnique Statistique." Moscow, Russia:MIR,1984 [5] "Topogaphy Obseving System Study," Studi Tecnologie Sistemi, Rome, Italy Tech.Rep.TR/ STS/001/97, Alenia Spazio Contact TLR/ALS/AR/19/96. [6] M.A.Sokosz, "On the Joint Distibution of Suface elevation and slope fo a non-linea andom sea with application to ada altimety," J. Geophysical Reseach, Vol.91, pp , Jan [7] G.S.Bown, "The Aveage Impuls Response of a ough Suface and its Application," IEEE T. Antennas Popagat., Vol.AP-5, pp.67-74, Jan [8] E.Rodiguez, "Altimety fo non-gaussian Oceans: Eight Biases and Estimation of Paametes," J.Geophys. Res., Vol.93, pp , Nov [9] D.E. Baich and B.J.Lipa, "Analysis and Intepetation of Altimete sea Echo," Adv. Geophys.,Vol.7, pp.60-99,1985. [10] G.Picadi et alii "Mas Advanced Rada fo Subsuface and Ionosphee Sounding (MARSIS)," T.R. n. MRS-001/004/99, Oct.99. [11] V.U.Zavootny and A.G.Voonovich "Scatteing of GPS Signals fom the Ocean with Wind Remote Sensing Application" IEEE T. [1] M.Migliaccio, M.Sati On the electomagnetic Scatteing fom Wind-Roughened Wate Suface /00/ IEEE [13] G.Bogo et alii Dopple Beam Shapening in Bistatic altimete Infocom T [14] M.Matin Neia A passive eflectomety and intefeomety system (PARIS): application to ocean altimety ESA J. Vol.17 pp , 1993 [15] Picadi et. al. : "Estimation o suface slope and eflectivity base on pocessing o ada altimete data", IEEE National Rada Confeence, Wakefield -Boston (Ma), ApiI 0-, 1993 [16] H. Came: "Mathematical Methods of Statistics", Pinceton Univesity Pess, 1958 [17] F.W. Ulaby, R.K. Mooe, A.K. Fung: "Micowave Remote Sensing -Active and Passive vol.ii, Atech House Micowave Libay 1986 [18] L.Petone, G.Picadi, E.Rocca, R.Seu, P.T.Melacci Multilook techniques and simulation softwae applied to the DBS Bistatic Altimetes - Oppscat WP400 Mid-Tem Repot Infocom T.R B. [19] Willis N.J., Bistatic Rada, Atech House, RTO-MP-SCI-150 UNCLASSIFIED/UNLIMITED

14 UNCLASSIFIED/UNLIMITED Bistatic Space Bone Rada fo Ealy Waning [0] Livingstone et alii, An aibone SAR expeiment to suppot RADARSAT- gound moving taget indication (GMTI), Can. J. Remote Sensing, Vol. 8, No. 6, 00 [1] Picadi G. et alii, Bistatic Model of Ocean Scatteing, IEEE T. Antennas Popag., Vol. 46 No.1, Oct. 98 [] Wang H., Mainlobe clutte cancellation by DPCA fo space-based adas, IEEE, 1991 [3] Picadi G., Masdea A, SBREW with Bistatic solution, STS, Technical Repot Febuay 005. RTO-MP-SCI UNCLASSIFIED/UNLIMITED

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16 Symposium on "Integation of Space-based Assets Within Full Spectum Opeations" Bistatic Space Bone Rada fo Ealy Waning G.Picadi, A.Masdea (STS) L.Tofone (Italian MoD) L.Bogaelli, L. Ceeoli (Alcatel Alenia Space) Coloado Spings 10-1 Octobe 005

17 Scenaio Geo-political evolution of ecent yeas has changed balance set up woldwide fom Cold Wa ea. Ethnic-cultual-eligious movements have pushed towads claims not canalised within democatic pocesses. Pessues have been geneated to westen wold, giving ise to oigin of movements with teostistic ends and hostile county too. Cush down of easten wold and economic powes has spead out knowledge, developments and e-cycling of old amaments. Risk of potential attacks to Euope o against euopean foces out of the continent has inceased. Awaeness of impotance of ballistic missile defence has set up. In paticula Regional Ealy Waning System study in Euope is going to be assessed. Coloado Spings, 1 Octobe 005

18 Why Space Assets? Difficult to jam. It is difficult to jam its capabilities. Use Pemises Sevices. Small eath stations with small antennas can povide access to databases, banch offices, and management infomation systems. Continuous opeability. Wideband Capability. Satellite epeates ae usually wideband devices that can tansmit lage amounts of infomation. Tens of megahetz of bandwidth ae available in each epeate. Boad Coveage. Technically, it can seve any type of station in view of its antenna. Bette Coveage of Rual and Undeveloped Aeas. It can povide the same type of sevice in evey situation. New Sevices. It can povide the meging of diffeent types of data to bette exploit event infomation. Coloado Spings, 1 Octobe 005 3

19 Needs fo Missile Defence Theate aea suveillance within a wide aea suveillance coveage. Continuos coveage (o vey low pecentage of gap). Engagement of the theats (detection, plot and tack) within a theate aea. Estimation of launch point. Estimation of final impact point (taget) of the theat. Delivey of the theats kinematics chaacteistic, within a defined basket, to the gound based ada fo the immediate defence eaction. Identification and classification of the theat. System achitectue based on multiple-senso (IR and EM) capabilities and data fusion. Coloado Spings, 1 Octobe 005 4

20 Dive Paametes Cisis Aea Extension Access Aea Cisis Aea Revisit Time Communication and Data Dissemination Infomation Age Spatial Accuacy Taget Chaacteistic Detection Delay Time Localization Accuacy Taget Image Reconstuction Capability False Alam Detection Pobability Tajectoy Measuement Capability Max Nume of Simultaneous Taget Speed Measuement Accuacy System Availabilty Reconfiguation Capability Coloado Spings, 1 Octobe 005 5

21 Available Waning Systems Technologies Senso Tade-off fo Missile Defence Applications ae on: INFRARED Themal IR instument is capable in missile detection duing boost phase. It suffes fom weathe conditions. MICROWAVE Rada instument is less sensistive to weathe conditions. Due to clutte, detection of missile in the boost phase can be difficult. Rada senso is capable to povide good and accuate tacking. UV-VIS They can be used in the suveillance fo suppoting intelligence activities. They suffe fom weathe conditions. In all of the thee types of taget, identification capability can be based on thei spectal signatue. Coloado Spings, 1 Octobe 005 6

22 Space Bone Rada fo Ealy Waning This study is addessed to analyze the equiements and a pope design of a space bone Bistatic SAR (BSAR) with the elevant pefomance. The bistatic solution has been consideed as a pefeed one due to the good immunity to potential jamme pesent on the theate aea, allowing also a educed value of peak tansmitte powe, pemitting to utilize quite all the tempoal inteval fo the signal tansmission without inteuption duing the eceiving phase. The BSAR technique pemits to incease the esolution in ode to disciminate closely tagets. In addition it has been investigated the imaging of an isolated fast moving pointing object (MPO) and the clutte cancellation needed in pesence of fixed teain/sea backgound (featue expected in the ealistic situation of an object moving ove a teain o ove the ocean). Coloado Spings, 1 Octobe 005 7

23 Refeence Requiements - System Minimum Taget RCS 0. m Rada Coss Section will fluctuate accoding to Sweling case 1; Altitude within 50 Km- 400 Km fo TBM, 00 m- 400 m fo cuise missile (option) and 00 m- 10 Km fo aicaft; Maximum ange fo TBM 3500 km; Time of flight fo TBM < 15 minutes; Aveage absolute velocity fo TBM.5 km/sec ; Delivey of the taget position within a basket of km. In case of tacking on boad (plot association, tack fomation) the esolution (discimination of closely taget) must be within 1 km; Jamming pesent on boad enemy aicaft and on enemy gound based ada. Pesence of Gound/Sea clutte; Coloado Spings, 1 Octobe 005 8

24 Tade-off Activities Thee configuations have been peliminay consideed and envisaged as potential candidates fo a design baseline: Tansmitte on boad heo satellite and eceive only on boad the satellite constellation. Tansmitte and eceive on boad each satellite on the constellation. Monostatic solution. Fist solution was chosen because of good immunity to potential jamming and educed complexity of constellation. Dawback is the ange between the tansmitte and the illuminated taget and the equied synchonization. In addition, a diect communication link between the tansmitte and the eceive is necessay. Majo constaint on the system configuation (ada and satellite constellation) is the minimization of numbe of satellites. Such minimization may be povided by use of ScanSAR techniques. Coloado Spings, 1 Octobe 005 9

25 Challenges & Basic Constaints Majo challenges elated to taded-off solution ae: Lage numbe of SATS (small sats shall be employed fo the constellation). Lightweight MW instuments. High powe needed by the Tx appaatus on boad HEO satellites. Constellation synconization. Inteopeability and infomation management. In ode to achieve a feasible solution, few constaints have been assumed, consideing the pesent and futue (next 10 yeas) state of the at technology: The maximum available tansmitting powe cannot be geate than 75 KW fo pactical easons. The antenna dimension should be limited to 15 m 15 m. A fequency utilization within the L band (1 GHz) has been selected as a good tade-off between loss and components availability (antenna and tansmitte). Coloado Spings, 1 Octobe

26 Typical Missile Tajectoy Coloado Spings, 1 Octobe

27 Reconciliation Coloado Spings, 1 Octobe 005 Intecept cmd 1data

28 SBREW Requiements - Obsevation The objective is to define a system able to alet defense countemeasues though pope taget detection and tacking. The Ealy Waning system is equied to opeate ove a squae-shaped aea called access aea (Nominally 1500 km x 1500 Km). 40 N 0 N Access aea can be selected within a lage aea called coveage aea (nominally fom Atlantic to Indian ocean and at low latitudes above the equato). Continuous obsevation of the access aea must be guaanteed with a minimum time lag between successive obsevations and compatible with the theat chaacteistics. 0 W 7000 km 9000 km 70 E Access Aea 000 km Coveage Aea Equato 000 km Coloado Spings, 1 Octobe

29 SBREW Design (bistatic( constaints) The tagets fo which the sum of distances with the two antennas is constant, cannot be esolved in ange by the bistatic system. The positions of these tagets located on the suface constitute an ellipse ( isoange contou ) It has to be highlighted that the tajectoies of Rx and Tx can be positioned in any diection. Futhemoe, due to Rx cicula obit and Tx elliptic obit, thee is a adial velocity component that is necessay to be compensated (only duing the tacking phase). Thee ae two exteme cases: Rx and Tx tajectoies ae paallel and diected othogonally to the dawing (assumption made in the pape). Rx and Tx tajectoies ae in the same plane and each one is diected towad the othe. RX α h α v Rx R 30 R 31 z R 10 v T TX x α α α y Coloado Spings, 1 Octobe x R 11 α t h t

30 Engagement & Tacking The taget engagement includes the following phases: Taget acquisition (only detection while plot and tack extaction will be pefomed by the on gound ada). Delivey to a gound ada of the static and cinematic paametes fo a fast eaction. The acquisition phase is a continuous pocess (multiple taget detection equiement) while the tacking pocess will stat, afte the detection, fo each taget. One of the objectives is to disciminate two o moe tagets inside one esolution cell duing acquisition phase. This can be done by synthetic apetue adas. N 1500 Km Tacking pocess is implemented though synthetic apetue technique. In ode to keep antenna dimensions into easonable values, a multilook technique shall be adopted. To cove the whole theate aea, with an acceptable esolution, ScanSa technique is implemented Nc 1500 Km Coloado Spings, 1 Octobe

31 Engagement & Tacking The ange compession gain can be witten as Bτ whee B is the tansmitted chip bandwidth (the same on which the noise powe is evaluated) and τ is the pulse duation. Theefoe afte ange compession we obtain: SNR Pp At A 4πλ σ τ = Rt R KTFL Once fixed the system geomety and achitectue, pulse width may be dimensioned accoding to desied SNR. In ode to avoid the clutte in the main lobe of the eceive antenna we can point the antennas at a highe altitude. Moving objects will be displaced between the two scenes and these displacements can be measued as phase shifts. Coloado Spings, 1 Octobe

32 Conclusions The baseline solution, that suggests the best tade off pefomance feasibility, is a bistatic solution (pesence of jamme on enemy ada) with the tansmittes on HEO/GEO and the eceives on LEO constellation (on boad LEO only eceive and on boad HEO/GEO only tanmitte). The Phased Aay technology shall be applied. By the system point of view the task of the ealy waning pocess is the taget engagement that can be divided into acquisition and tacking. The detection pocess will be pefomed on a single (o multiple when possible accoding to the scanning time of the theate aea) spot basis due to the absence of infomation on the taget tajectoy. The tacking pocess will follow the detection on a SAR basis, in ode to incease the esolution, being possible the estimation of the taget tajectoy and theefoe the pocessing with a suitable selection of dedicated filtes. Fo the satisfaction of the system equiements the tacking is not equied due to the assumed value of the antenna dimension. The tacking phase (SAR) is a good option fo the discimination of closely spaced tagets. Coloado Spings, 1 Octobe

33 Conclusions The Signal to Noise atio (SNR) is a citical paamete, consideing the satellites geomety (ange) and the limited value of tagets ada coss sections. Futhemoe, the SNR is stongly elated to the powe density on the taget and theefoe to the swath dimension (TX and RX antennas gain). The theate aea is too much extended to be coveed with a small numbe of satellites. Resolution equiements, fo the taget spatial identification, ae in good ageement with the beam dimension duing acquisition and also duing tacking, due to the impovement facto, elated to the implementation of the Synthetic Apetue concept (SAR), taking into account the integation of a cetain numbe of pulses (defined by the time needed to geneate the synthetic antenna efeed to the PRF). The high tansmitte powe is definitely a heavy constaint as well as antenna dimensions. Coloado Spings, 1 Octobe