Monitoraggio Geodetico e Telerilevamento 3 Remote Sensing Images Carla Braitenberg Dip. Matematica e Geoscienze Universita’ di Trieste berg@units.it Tel. 339 8290713 Tel. Assistente Dr. Nagy: 040 5582257

View of Earth surface

Viewed area changes from circle to ellipse at off-nadir veiw angles

Immagine proiettata da una lente ogetto Punto focale Punto focale Immagine Per un rivelatore di dimensioni finite, l’immagine maggiore che posso rappresentare E’ definita dalla lunghezza focale f della lente.

Examples for Whiskbroom and Pushbroom scanners Landsat Multispectral Scanner (MSS) Landsat Thematic Mapper (TM) Landsat 7 Enhancement Thematic Mapper (ETM+ ) Pushbroom Landsat 8 Operational Land Imager (OLI) and Thermal Radiation Sensor (TIRS)

From Landsat7 Handbook Optical path for Landsat 7 across track scanning image acquisition system.

From the handbook, description of previous figure Scene energy passes through a number of major ETM+ subsystems, depicted in Figure 3.2, before the solid-state detectors at the focal plane collect it. The bidirectional scan mirror assembly (SMA) sweeps the detector's line of sight in west-to-east and east-to-west directions across track, while the spacecraft's orbital path provides the north-south motion. A Ritchey-Chretien telescope focuses the energy onto a pair of motion compensation mirrors (i.e. scan line corrector) where it is redirected to the focal planes. The scan linecorrector is required due to the compound effect of along-track orbital motion and crosstrack scanning which leads to significant overlap and underlap in ground coverage between successive scans. The aligned energy encounters the Primary Focal Plane (PFP), where the silicon detectors for bands 1-4 and 8 (panchromatic) are located. A portion of the scene energy is redirected from the PFP by the relay optics to the Cold Focal Plane where the detectors for bands 5, 7, and 6 are located. The temperature of the cold focal plane is maintained at a predetermined temperature of 91° K using a radiative cooler. The spectral filters for the bands are located directly in front of the detectors.

From Landsat8 Handbook Landsat8 OLI and TIRS sensors arrangement.

Landsat 8 pushbroom sensor OLI (Operational Land Imager) instrument Sensor Chip Algnment (SCA) in focal plane. Each SCA contains rows of detectors.

Continues Landsat 8- redundant arrangament of sensitive devices to have sensor backup.

Thermal infrared sensor Landsat8 TIRS arrangament of sensors in the focal plane.

Dwell time comparison Whiskbroom Landsat TM Pushbroom Time for one cross track sweep: T=w/v w= down track pixel size (30m) V=satellite velocity (7500 m/s) Dwell time for one pixel: dT=T*dL/L L: Cross track line width (185000 m) dL: cross track pixel size (30m) dT=6.5 10^-7 sec/pixel Pushbroom Dwell time dT=w/v With the values of left side: dT=20 sec/pixel No reduction through cross track sweep.