THE PHYSICS OF BISTATICAL RADAR METHODS OF OCEAN REMOTE SENSING

1. EARLY DISCOVERY OF DANGEROUS PHENOMENA IN THE OCEAN Sergey V. Pereslegin P.P. Shirshov Institute of Oceanology RAS, MoscowLeon B. Neronsky Joint-Stock Radio Engineering Corporation «VEGA» Moscow THE PHYSICS OF BISTATICAL RADAR METHODS OF OCEAN REMOTE SENSING

2. CONTENS 1. The problem statement: the main requirements to “panoramic radio-altimeter”, their prototypes, the objects of radar diagnostics. 2. The singularities of radar two-positional (bi-static) scattering mechanism: “a light track” sensing regime. 3. The optimum variants of space radar system 4. The physical basis of two-positional InSAR for diagnostics of ocean phenomena. 5. The parameters of space InSAR: prototypes and proposed variants. 6. The main results and recommendations.

3. The survey objects, the requirements to radar system The main objects: • Swell • Tsunami in open ocean • Spatial and temporal structure of wind waves, internal waves and ocean currents. The main requirements: • Swath width of about 1000 km • Revisit time no more of 1 hour for given ocean region • Horizontal resolution for seismic waves ~1 km with vertical resolution ~10 cm • Horizontal resolution for swell ~20 m with vertical resolution ~1m • Radiometric resolution ~1 dB on the area (100x100) m²

4. Monitoring of seismic waves and early discovery of tsunami in the ocean

5. Existing and on-going radar tools, their possibilities with observing of ocean dangerous phenomena 1. Radioaltimeters: use of the economic “quasi-mirrow” regime, allows the monitoring of long-scale ocean level field. The revisit time is ~30 day with one spacecraft. The project of JPL (nadir - InSAR) allows to have ~ 6 day with swath width ~200 km. 2. MW-scatterometers: allowthe “indirect” monitoring of wind speed long-scale field (on the same regime). The images revisit time is ~1 day as for Quikscat. 3. One-antennas SAR: allows diagnostics the of small-scale ocean phenomena in given regions with revisit time ~ 3-5 days. 4. InSAR - Shuttle Radar Topography Mission (2001): allowed to restore the ocean level field, but its results are unknown for us. 5. The GPS systems for ocean level field observations are proposed within the GNSS program. Our opinion: the necessary parameters of ocean level images are impossible to have by this way.

6. Y , м Y/10 PROPERTIES OF TWO-POSITION REMOTE SENSING SYSTEMS

7. There is no difference between radar two-position properties and sun-glint

8. Two-position radar scattering diagramsfrom the ocean surface (Kharkov IRE, 1976) ψ1 – radiators elevation angle, ψ2 – receivers elevation angle, φ – receivers azimuth angle, S(φ,ψ2) – specific effective reflection area Our case: λ=3 cm, HH-polarization, φ=0, ψ1=25, ψ2=(125 – 175) with S from 0 dB to +15 dB

9. Two variants of two-positional spaceborne radar H1 = H2 , two small satellites with InSAR. The left or right satellite must be receiving in turn. H2 << H1 (geostationary satellite). Receiving InSAR exists on the orbit H2

10. Side-looking InSAR, two-positional regime.The correlation coefficient

11. Processing algorithm and leveling sensitivity

12. Side-looking InSAR, two-positional regime.The interplay of radar parameters and energetic. In comparison with one-position space InSAR: • Swath width about (1-1,5)H2 with the better energetic and without the multi-beam regime • With the same a vertical resolution, a horizontal resolution is somewhat worse – besides the area near a mirror point, where its vastly worse • The permissible width of signal spectra, depending on power potential, is vastly more

13. Calculated parameters of one- and two-positional InSAR for the ocean level field observation

14. The main results 1. Two-positional space InSAR is special effective with restoration of ocean level field. 2. The main peculiarities two-positional InSAR are: • Increasing of survey width is no connected of range ambiguity • The effective energetic is the consequence of “quasi-mirror” scattering from the ocean surface. • A cross-track resolution is suddenly worsen near a mirror point, but it’s a workable for the most part of range direction. • With given size of an antenna basis and energetic potential, the width of signal spectrum is limited – this factor determines, in first turn, a leveling resolution. 3. Calculated parameters of spaceborne InSAR two-positional system of proposed variants – corresponds the main requirements for radar diagnostics of dangerous phenomena in the ocean based on measurements of the ocean level field.

15. The main recommendations 1. Conducted analysis and calculations show that the modern technologies allow to work up an effective and economic spaceborne radar system for early discovery of dangerous ocean phenomena. 2. Proposed variants of spaceborne two-positions InSAR – have to be developed in respect of radio-technical problems. The main problems are: a development of receiving antennas with a rigid cross basis and a maintenance of necessary power energetic (only for geostationary satellite). 3. Before development of radar systems – all aspects of developments and applications of space two-position InSAR, including development and testing of airborne prototypes – must be investigated.