6/21/10 Ionospheric mitigation schemes and their consequences for BIOMASS product quality O. French & S. Quegan, University of Sheffield, UK J. Chen, Beihang University, China ESA, Holland, 4th March 2010 Task 100: Database of Ionospheric Scenarios

6/21/10 Overview 1. Limitations of initial strategy 2. Modified strategy 3. Deliverables a. database; b. simulation codes; c. technical note 1; 4. Technical issues and scope of software 5. Further work 6. Effect of orbit local time upon ionospheric scintillation 7. Relation of TEC fluctuations to FR 8. Use of GPS TEC database

6/21/10 Limitations of Initial Strategy Original proposed approach was to generate database of ionospheric phase screens Limitations: a. Computationally onerous b. Large data storage requirements c. Inflexible d. Redundancy e. Can only be performed at UoS

6/21/10 Modified Strategy To generate a database of the WBMOD output To provide codes that can run simulations using the above database Advantages over previous methodology a. More flexible b. Reduced data storage requirements c. Time savings d. Reduced redundancy e. ESA can run on site

6/21/10 Deliverables: Database Database entries for the following scenarios: ParameterValues contained within databaseParameter type Satellite altitude (km)650 Satellite Antenna length (m)20.16Satellite Orital inclination (°)98Satellite Frequency (MHz)435Satellite Orbital node typedawn duskSatellite Look angle (°)+30 (night) -30 (day)Satellite Planetary index, Kp Ionosphere Ck confidence interval (%)99.0 Ionosphere Date inclusive at 10 day intervals Temporal Satellite latitude (°)-80 to 80 inclusiveSpatial Satellite longitude (°)-180 to 180 inclusive Spatial

6/21/10 Deliverables: Database Each entry comprises the WBMOD output for: a. Satellite locations between ±80°N at 1° resolution in latitude and longitude. b. Fixed equatorial local time throughout a single date c. A specific set of ionospheric and satellite parameters See Technical note 1 for full list and definitions of WBMOD parameters.

6/21/10 Ground Latitude Ground Longitude log10 {CkL} Global map for 99th percentile of log10 CkL Night-looking dawn node on 1/1/1995 and Kp = 1

6/21/10 Deliverables: Simulation codes Runs simulations of ionospheric phase screens for a particular scenario: a. Location b. Time c. Ionospheric conditions d. Orbit configuration Codes draw the WBMOD data required for a given simulation from the database. See Technical note 1 for full description of simulation codes and their operation.

6/21/10 Deliverables: Simulation codes Data outputs: 2D phase screens Range autocorrelation Azimuth autocorrelation 1D phase slices Point spread functions Metrics Statistics Phase screen geometry:

6/21/10 Deliverables: Simulation codes Ly (km) Lx (km) Phase deviation

6/21/10 Deliverables: Simulation codes Phase deviation (rad) Azimuth (km)Azimuth (m) Normalised PSF

6/21/10 Scope of codes Run Times On the University of Sheffield servers, 100 phase slice realisations for a given scenario takes approx. 30 minutes. This can vary depending on the number of 1D phase slices extracted from each Limitations Memory constrains maximum side length of square phase screen to be twice synthetic aperture

6/21/10 Further Work Simulation of 1D phase screen Length of simulation extended at expense of full 2D correlations (ongoing) Full study of 2D correlation 2D autocorrelation function given by Rino 1979 Can be calculated from WBMOD output Extent of decorrelation will dictate retrieval algorithms

Click to edit Master subtitle style 6/21/10 Effect of orbit local time Locations covered: Boreal (BO): Sweden Temperate (TE): Austria Equatorial (EQ): Borneo

Click to edit Master subtitle style 6/21/10 Effect of orbit local time Orbital parameters used: Altitude = 650km; Inclination = 98°; Look angle = 30° (night looking); Frequency = 435 MHz; Antenna length = 20.16m (Concept 2 of BIOMASS RfA). Ionospheric conditions: date = 21/6/2000, close to solar maximum; KP = 3 (electron precipitation boundary at 61.2°MagN); log10CkL percentile = 99%;

Click to edit Master subtitle style 6/21/10 Effect of orbit local time Satellite node is defined by its local time (LT) as it passes the equator Orbital nodes considered: o Dawn ascending 05:00 06:00 07:00 o Dusk descending 17:00 18:00 19:00 Away from equator LT deviates from its equatorial value

Click to edit Master subtitle style 6/21/10 Effect of orbit local time Local Time 18:0 0 06:0 0 Later

Click to edit Master subtitle style 6/21/10 Effect of orbit local time Boreal location: Sweden (17°E, 65°N) High disruption for all nodes; CkL ≈ 1033 Little variation with orbit local time Ly (km) Lx (km) One-way phase deviation f Azimuth distance (m) Point spread function 06:00

Click to edit Master subtitle style 6/21/10 Effect of orbit local time Equatorial location: Borneo (115°E, -2°N) Little disruption to PSF for all dawn nodes, and 17:00 and 18:00 nodes. CkL ≈ 1031 Ly (km) Lx (k m) One-way phase deviation Point spread function Azimuth distance (m) 18:00

Click to edit Master subtitle style 6/21/10 Effect of orbit local time Equatorial location: Borneo (115°E, -2°N) Large disturbance for 19:00 node post-dusk region → high fluctuations, CkL ≈ 3.6 x 1035 Ly (km) Lx (km) One-way phase deviation Azimuth distance (m) Point spread function 19:00

Click to edit Master subtitle style 6/21/10 Effect of orbit local time Equatorial location: Borneo (115°E, -2°N) Satellite is night looking – looking into the region of high ionospheric fluctuation Effect disappears for the 19:00 orbit when day looking configuration is used Looking away from region of high fluctuation Temperate location: Austria (12.5°E, 47°N) Little disruption for all nodes; CkL ≈ 1031 Little variation with orbit local time

Click to edit Master subtitle style 6/21/10 Effect of orbit local time Summary General trends as LT moves from night to day: Increase in mean TEC and FR; Decrease in ionospheric fluctuations (CkL). Post sunset equatorial zone: Pronounced increase in CkL for 19:00 night-looking node Can be avoided by using day-looking setup Boreal zone is a problem under all circumstances.

Click to edit Master subtitle style 6/21/10 TEC fluctutations & FR Phase fluctuation, φ (rad), is related to TEC (TECU) via and FR, Ω (rad) to TEC by [1] Therefore [1] Belcher, D.P. Theoretical limits on SAR imposed by the ionosphere, IET Radar Sonar Navig., 2, (2008)

Click to edit Master subtitle style 6/21/10 TEC fluctutations & FR For BIOMASS, f = 435 MHz and this reduces to and for Bm = 3.5 x 10-5 T Meaning that a phase fluctuation of at least 445° is required to achieve a fluctuation of 1° in FR. Is this beyond measurement capabilities?

Click to edit Master subtitle style 6/21/10 Use of GPS data Various sources of GPS TEC data: Centre for Orbital Determination in Europe (CODE) International IGSS Service (IGS) - includes CODE Longitude -180° to 180° E 5° resolution Latitude -87.5° to 87.5° N 2.5° resolution Time From 1992 onwards 2 hours resolution

Click to edit Master subtitle style 6/21/10 Use of GPS data Centre for Orbital Determination Europe (CODE) data Accuracy of ±3.5 TECU Thorough statistical analysis ongoing