Ship traffic monitoring may be performed using satellite SAR data. The advantage with the SAR sensor is the all
weather and day/night imaging capability. However, the SAR backscatter contrast between a vessel and the
surrounding sea state may be small in high wind conditions and at small incidence angles. The present and future
SAR satellites will have the capability of imaging the earth surface with several incidence angles, and with dual-polarimetry
(HH/HV, VV/VH or HH/VV). The SAR ship/clutter contrast may threrefore be increased by applying
different polarisation combinations, or using higher incidence angles.
We have shown that geocoded ENVISAT ASAR images in the coastal region of Norway can be used to gain
experience in the combined use of satellite SAR and an automatic identification system (AIS) for ship traffic
There are plans for placing AIS systems onboard satellites. It will then be possible to fuse the information from
satellite SAR with those from satellite (or ground-based coastal) AIS and thereby identify all the detected ships
within a SAR image. This data fusion will enable us to develop further knowledge about SAR backscatter properties
from vessel types that may not be detected so well using the SAR data only. On the other side, it will be possible to
pin-point those ship candidates that do not carry an AIS system, and thereby take appropriate security or rescue
The signal to clutter ration of targets in Synthetic Aperture Radar (SAR) images is a function of the resolution cell and the backscattered radar cross section (RCS) of the target where both the resolution cell and the RCS of the moving target are a function of the time. Due to the long integration time both the SAR look angle and the spatial reflection pattern vary during the integration. Hence, there exist a complex interaction between the spatial reflection pattern, the temporal variation of the moving target, the long integration time and the varying platform look angle. This complex interaction gives an upper and lower limit to the size of simple scatterers such as flat plates. An attempt has been made to try and assess the size and geometry of typical main scatterers of a generic maritime target in order to predict the imaging capabilities of the soon to be launched ENVISAT SAR.
Satlantic and Orbital Sciences Corporation have developed a concept for a novel satellite scatterometer mission designed to retrieve the global marine wind fields on a daily basis. Using a constellation of 5 - 8 small satellites in low earth orbit, each equipped with a Ku-band scatterometer, ocean basin wide winds could be observed synoptically on time scales consistent with 12 hour weather forecasts. Traditional approaches to design of marine wind scatterometers have been based on the concept of providing a swath, e.g., 500 km wide for ERS-1, which produces bands of dense (25 km spacing, 50 km resolution) observations over the oceans. The observation frequency varies according to repeat cycles, orbit phasing and latitude. On the other hand, global forecast models generally have grids at the same or lower resolution, but evenly spaced. The mismatch in the measured fields with those of the models has reduced the utility of using satellite derived winds for operational data assimilation. The present concept is based on the premise of sampling the winds on a scale more consistent with the current generation of medium term forecast models. The observations would be assimilated into these models, and would provide more stable solutions or model states on which to provide forecasts. The scatterometers are designed to be scanning, pencil beam systems, configured with three beams looking to each side. The scanning is carried out in a fashion that allows a patch on the ocean to be observed at 4 different azimuthal angles, thus providing good resolution of directional ambiguity. Data processing is very simple, avoiding range gating or Doppler processing. The resulting downlink data rates are also low enough to allow the design of a simple, low-cost ground segment that would be designed for ease of assimilation of the global wind fields into operational models in near to real-time.