NovaSAR-1 User Guide
Welcome to the NovaSAR-1 User Guide
This User Guide provides a description of the NovaSAR-1 specifications, modes and products. It also gives information on the calibration, orbit characteristics and compatible software.
Last updated: October 2020
Use the following links to navigate your way around the user guide:
- Overview A brief description of the mission and SAR technology.
- Satellite Specifications Defines the main mission characteristics.
- S-Band SAR Provides information on S-band and comparisons to X, C and L-Band.
- Automatic Identification System (AIS) Describes the AIS secondary payload.
- Baseline Acquisition Modes Describes the NovaSAR-1 acquisition modes: Stripmap, ScanSAR, ScanSAR Wide and Maritime.
- Imaging Characteristics This section has information on Polarisations, Pass Direction and Antenna Pointing.
- Revisit and Coverage Provides details on the NovaSAR-1 Orbit characteristics, revisit and coverage.
- Product Types and Processing Levels Describes the processing levels in which NovaSAR-1 products are provided.
- Naming Conventions Describes the data naming conventions used for NovaSAR-1 product folders and files.
- Data Formats and File Types Describes the data formats that NovaSAR-1 products are distributed in.
- Calibration and Validation Outlines the procedures used in the calibration of NovaSAR-1 data.
- Compatible Software Lists the software programs with readers available for processing NovaSAR-1 data
NovaSAR-1 is a joint technology demonstration initiative of SSTL (UK) and Airbus DS (former EADS Astrium Ltd, Stevenage, UK), funded by the UK Government via the UKSA (UK Space Agency). The overall objective is to make SAR (Synthetic Aperture RADAR) observation missions more affordable to a customer base and to open up new applications in the S-band microwave region of the electromagnetic spectrum.
NovaSAR-1 is a much smaller version of traditional spaceborne SAR sensors, with a mass of 450 kg. It was developed to be low-cost whilst still providing medium resolution data with wide coverage. This is achieved by:
- Reuse of heritage avionics (satellite platform) based upon the SSTL 300 avionics (used for Nigeriasat-2) to reduce risk.
- Compatibility with existing SSTL satellite ground control segment.
- The payload back-end comes from existing Airbus Defence and Space UK instrument architecture.
- Use of COTS technology where suitable to reduce cost.
The SAR payload operates in the S-band microwave frequency (3.2 GHz), corresponding to a 9.4 cm wavelength and can operate in four operational modes. The spacecraft is also equipped with a secondary Automatic Identification System (AIS) payload produced by Honeywell Aerospace that can be combined with NovaSAR-1’s maritime surveillance mode for ship identification.
What are the benefits of RADAR imaging?
Radio Detection and Ranging (RADAR) is an active imaging technology in which pulses of microwave energy are emitted from an antenna and the resulting reflections are used to create images. Some advantages over optical imaging include:
- The ability to image day and night as the active SAR system does not rely on sunlight.
- The signal can penetrate clouds, rain, dust and even volcanic ash, providing imagery where traditional optical imagery would fail.
- Depending on the signal wavelength, SAR can image through the vegetation canopy.
- The lens is not fixed therefore the sensor is flexible regarding resolution and ground coverage.
What is Synthetic Aperture RADAR?
Synthetic Aperture RADAR (SAR) uses the different locations of the sensor, as it moves along the flight path, to simulate a large antenna from a smaller one. This enables SAR sensors to provide high-resolution imagery that does not degrade with distance like traditional RADAR systems with large antennas.
For detailed information on SAR visit our Resources page
- Satellite Specifications
NovaSAR-1 Mission Characteristics Parameter Value Imaging frequency band 3.1-3.3GHz (S-band) Antenna Microstrip patch phased array (3m x 1m) No. of phase centres 18 Peak RF power 1.8kW Polarisations HH, HV, VH, VV Design life 7 years Mass 450kg Orbit 583km SSO 1030am LTAN Propulsion system Xenon-based Payload duty cycle 2 min per orbit Payload data memory Up to 256 GBytes Downlink rate 400 Mbps Downlink frequency band X-band (8.025-8.4 GHz) TTC frequency band S-band (2025-2110 MHz, 2200-2290 MHz) Geolocation <50 metres
- S-Band SAR
The NovaSAR-1 SAR payload uses the S-Band frequency range, which is less common in spaceborne SAR systems than the X-, C-or L-bands.
S-Band SAR imaging has already proven utility onboard the Russian Kondor-E1 (2013) and Almaz-1 (1991) satellites and the Chinese HJ-1C (2012) satellite. It is the selection of S-Band that makes NovaSAR-1 possible, as the efficiency of the new Gallium Nitride amplifier technology offers higher conversion of energy to radio-frequency and produces far less surplus heat than those amplifiers currently used for X-, C- and L-Band satellites.
NovaSAR-1 S-band imagery offers many advantages over other SAR frequencies:
- It can image in areas of high rainfall as it is not subject to rain shadowing which has been shown to be a problem at X-band.
- Better ground penetration than higher frequency C- and X-bands – potentially useful for detection of variations in soil moisture and detection of sub-surface features.
- Shows discrimination between different vegetation structural types, due to greater penetration through the upper canopy layers, making it effective for vegetation monitoring, land cover classification, and forestry analysis.
- The effect of Faraday Rotation (i.e. the rotation of the polarisation vector of a radio wave propagating through the ionosphere which results in a reduction backscatter levels) is minimal using S-band compared with standard L-band sensors.
Comparison of SAR bands
SAR bands comparisons Frequency Band Frequency Range Wavelength (cm) Example Spaceborne SAR Systems (past, present, planned) Typical Applications/Strengths P-band 43.2-438 MHz 68.5-69.4 BIOMASS High penetration, detection of targets concealed by foliage or camouflage, buried object, archaeological, estimates of biomass, map forest disturbances. L-band 1215-1300 MHz 23.1-24.7 SEASAT, JERS-1, ALOS PALSAR, ALOS-2 PALSAR-2, SAOCOM-1A/1B, NISAR-L Good penetration, land applications – forestry, environmental monitoring, agriculture, geology, hydrology. S-band 3.1-3.3 GHz 9.1-9.7 ALMAZ-1, HJ-1c, KONDOR-E, NovaSAR-1, NISAR-S Ship detection, ice mapping, oil spill detection, flood mapping, forestry mapping, crop classification. C-band 5.25-5.57 GHz 5.4-5.7 ERS-1/2, Envisat ASAR, Radarsat-1/2, RCM, Sentinel 1A/B Sensitive to ocean features, ship detection, sea ice surveillance, oil spill monitoring, crop classification. X-band 9.5-9.8 GHz 3.1-3.2 TerraSAR-X/TanDEM-X, COSMO-SkyMed, IGS-1B/3B, TecSAR, RISAT-2, PAZ, KOMPSAT-5, SAR-Lupe Sensitive to surface roughness, high-resolution applications, topographic mapping, flood mapping, early-stage crop growth.
- Automatic Identification System (AIS)
NovaSAR-1 is the first civilian SAR to have an AIS receiver on-board at the same time. AIS is a Very High Frequency (VHF) system, designed for the automated location and tracking of vessels. AIS transceivers are fitted on international voyaging ships with a gross tonnage greater than 300 tons and all passenger ships. Messages report a minimum of:
- the vessels unique identifier
These messages are transmitted at least every 30 seconds for ships in motion (up to every 2 seconds for fast-moving or manoeuvring vessels) and no less than every 3 minutes for ships at anchor. The AIS receiver onboard the NovaSAR-1 platform can be used to collect data just before and after the SAR imagery of the same area, providing additional information on the identification of detected ships and highlight non-AIS transmitting vessels.
The AIS receivers are the next generation receiver from Honeywell and are a Direct Radio Frequency Sampling (DRFS) type with support for two antenna interfaces sampled by high-performance A/D converters and clocked by a low-noise https://aerospace.honeywell.com/high-stability clock. The receiver supports 6 AIS channels that include:
• Channels 1 and 2 (161.975MHz and 162.025MHz) are the currently operational AIS channels
• Channels 3 and 4 (156.775MHz and 156.825MHz) that have recently been allocated to space-based AIS
• Channels 5 and 6 (161.950MHz and 162.000MHz)
Each AIS receiver has 2 orthogonally mounted antennas that provide near omnidirectional coverage that will provide instantaneous coverage of approximately 20 million km².
For technical information on the Honeywell AIS-MS03 Receiver Download PDF
AIS Product Format
- .ais – as downloaded binary with a CCSDS timestamped header appended to each demodulated AIS message
- .xml – AIS messages in NMEA-0183 text format
- Baseline Acquisition Modes
NovaSAR-1 offers a range of imaging modes with a variety of swath widths and imaging resolutions that can be chosen to best suit the needs of the user. All modes can be operated in either right-looking or left-looking antenna pointing directions and from an ascending (approx. South to North) or descending (approx. North to South) orbit.
- Imaging Characteristics
SAR systems can control the polarisation of the microwaves that are transmitted and received by the sensor. Features on the ground appear differently depending on which transmit and receive polarisations are used.
The NovaSAR-1 payload transmits both Horizontal (H) and Vertical (V) polarisations and can be operated in any of the four standard single polarimetric configurations:
- HH – for horizontal transmit and horizontal receive
- VV – for vertical transmit and vertical receive
- HV – for horizontal transmit and vertical receive
- VH – for vertical transmit and horizontal receive
The NovaSAR-1 payload receives one polarisation (H or V) at a time and switches between them for multi-polar modes. The instrument is therefore capable of providing incoherent, i.e. not exactly simultaneously, dual and tri polarisation. This alternating polarisation was also utilised on ESA’s Envisat.
The ScanSAR and ScanSAR Wide modes have a variety of polarisations available although VH is not currently included in any modes. Stripmap is currently available in single polarisation HH or VV only and Maritime mode only functions in HH.
NovaSAR-1 can image in both ascending and descending orbits.
NovaSAR-1 does not image at Nadir but can image with either left or right pointing of the antenna (also referred to as the look direction).
- Revisit and Coverage
NovaSAR-1 operates in a sun-synchronous orbit at 580km with an LTAN (Local Time of the Ascending Node) of 10:30. The satellite ground track can be seen below. Each orbit shifts to the west by approximately 24.3° of longitude at the equator. There are 15 revolutions a day resulting in 3-4 passes day over Australia.
NovaSAR-1 Orbit Parameters Parameter Value Repeat Cycle 14 days Revolutions per day 15 Period (Minutes per orbit) 97 minutes Revolutions per cycle 209 Ground track distance at the equator 192 km Ground track distance over Australia 138- 88 km Altitude 583 km Inclination 97.86 deg LTAN 10:30 Eccentricity 0.00165 km Semi Major Axis 6967 km Satellite Catalog Number/NORAD ID 43619
The repeat cycle (for the same mode and look direction) is approximately 16 days. However, NovaSAR-1 does not operate with a fixed orbit but has a slight drift (described above). This means it does not follow a path/row acquisition strategy like other satellites and therefore acquisition parameters over the same area will vary slightly between acquisitions, as shown below.
Due to the orbital shift, opportunities for interferometric measurements are ad-hoc and limited to archive image pairs with small enough spatial baseline. There is the potential to control the orbit over a short section of the satellite’s total lifetime to provide a demonstration interferometric capability but this would need agreement from all mission partners.
- Product Types and Processing Levels
Level-0 products consist of raw SAR data and are the basis on which all other level products are produced.
Level-0 products are not provided to users but are stored in the CSIRO archives so that they can be used to reprocess any level of product while the data is available.
Level-1 products are automatically produced by CSIRO using the software produced by the SAR payload manufacturer Airbus DS
Level-1 products are provided to users free and open-access without a proprietary period and are available in the following product types:
NovaSAR-1 Product Types Product Looks Range Applicable Mode slc Single Look Complex Slant Range Stripmap only srd Multi Look Detected Slant Range Stripmap only grd Multi Look Detected Ground Range Stripmap only scd Multi Look Detected Ground Range ScanSAR only
- Naming Conventions
The NovaSAR-1 product directory name is of the form:
- NovaSAR_sn indicates the platform from which the acquisition was made
- AcqID is the acquisition_ID, a numerical value which increases over time, the CSIRO archive will not contain a full sequence as other mission partners images use the same numbering scheme
- xxx indicates the Product Type and will be can be SLC, GRD, SRD or SCD
- date_time indicates the acquisition start time in the format YYMMDD_hhmmss
- polList indicates the set of polarisations used for the acquisition, this can be single polarisation e.g. _HH or a combination of polarisation e.g. HH_HV
As an example: NovaSAR_01_12737_scd_200706_160034_HH_HV.zip has Acquisition ID 12737 and is an SCD product acquired at 16:00:34 on 06/07/2020 with HH and HV polarisations.
- Data Formats and File Types
NovaSAR-1 products are distributed in a zip folder and consist of:
- One or more Image Product File(s)
- One or more Quick-Look Image file(s)
- One Metadata File
- One Metadata Stylesheet File
Image Product File
The Image Product file is in GeoTIFF .tif format and contains the image processed to the resolution specified for the imaging mode. Multiple Image Product Files will be present when:
- An image is comprised of multiple polarisations, in this case a file will appear for each polarisation e.g. image_HH.tif, image_HV.tif and image_VV.tif as below
- A single Image Product File would exceed the TIFF format 4 GByte limit. In this case the image is divided into equal slices as below
Quick Look Image File
The Quick-look Image file contains a coarser resolution version of the processed image, always in detected format (ie never complex). The coarser resolution is achieved using an adaptive subdivision process to average neighbouring pixels so that the image size is reduced to around 1K x 1K pixels. It is named QL_image_pol.tif where _pol indicates the polarisation for the Quick-Look image, ie _HH or _HV etc
The Metadata File is named Metadata.xml and logically records full information on SAR data acquisition, image generation and image characteristics. It enables full interpretation of the Image Product File.
A full description of the Metadata Parameters can be found here
Metadata Stylesheet File
The Metadata Stylesheet is named Metadata_style.xsl and provides formatting information for the Metadata file to a compatible web browser (eg Internet Explorer).
- Calibration and Validation
Calibration of NovaSAR-1 was undertaken by SSTL during the spacecraft commissioning and involved assessment of the following features against their expected values:
- Reference chirp
- IRF Sidelobe symmetry
- IRF PSLR
- Radiometric stability
- Radiometric correction across swath
- Pointing knowledge
These measurements will be repeated throughout the mission lifetime to identify any variation in performance.
Radiometric/geometric calibration using passive targets including:
- Rain forest (wide-area homogenous distributed targets)
- Calm water, salt flats and airport runways (low backscatter dark targets)
- Corner reflectors (known radar cross-section point targets):
- Radiometric stability
- standard deviation of 0.41 dB
- the metadata field “RadiometricScaling” indicates whether the image has be generated with beta nought, sigma nought or gamma nought scaling
- the metadata “CalibrationConstant” field can be used to convert the pixel integer value into a scaled value: Scaled pixel value = (pixel amplitude)^2 / CalibrationConstant
- Geometric accuracy
- the mission planning software uses an estimate of height (above the WGS84 earth ellipsoid model) at the middle of the image to plan the image. This height is written into payload configuration and the payload writes it into the raw data
- the image processing software uses platform orbit information, pulse timing, the WGS84 ellipsoid model of the earth and the height written into raw data to georeferenced images
- the height used for georeferencing is written into the metadata field “MeanTerrainHeight”
- for accurate geolocation of all points another tool must be used to perform terrain correction on the IFP output
- mission requirement for geolocation error is better than 50m (3σ) with respect to the reference Earth ellipsoid (without Ground Control Points and terrain correction).
- when geometric correction is applied to the data to account for the difference between the ellipsoid height used to generate the level 1 product and the actual terrain height, the geolocation requirement is easily achieved and is typically <10 m
- Compatible Software
NovaSAR-1 Data can be opened and processed using the following software:
- GAMMA produced by Gamma Remote Sensing – NovaSAR-1 Readers are available in Gamma
- ENVI SARScape produced by Harris Geospatial
European Space Agency SNAP toolbox (not all utilities are currently operational for NovaSAR-1 data, e.g. Geometric Terrain Correction )
The NovaSAR-1 Product Reader is available as a SNAP Extension which can be installed via (Tools->Plugins->Available Plugins). It can also be manually downloaded here
Instructions for installing the ESA SNAP toolbox and NovaSAR-1 reader plug-in
- Install the SNAP Sentinel-1 toolbox using the links above
- Install the NovaSAR-1 reader using:
Tools > Plugins > Available Plugins > NovaSAR Product Reader
- Check the plugin has installed by going to:
File > Import > SAR Sensors
More information on how to use NovaSAR-1 data in SNAP is available here