What once began as a highly controlled technology, only accessible to defense and intelligence organizations, is now open to the commercial world. Google Maps and MSN even brought satellite imagery to the computers and smart phones of consumers.
We see an abundance of satellites in orbit, covering a broad range of high-resolution and wide-area coverage. We also see many types of signals in use, with optical spectra still center stage, enhanced by infrared, hyper-spectral and radar signals.
Some of the imagery created is free-of-charge or available at relatively low cost.