Remote Sensing – Frequently Asked Questions
Remote sensing is the process of detecting and monitoring the physical characteristics of an area by measuring its reflected and emitted radiation at a distance (typically from satellite or aircraft). Special cameras collect remotely sensed images, which help researchers “sense” things about the Earth.
There are two types of remote sensing instruments—passive and active.
- Passive instruments detect natural energy that is reflected or emitted from the observed scene. Passive instruments sense only radiation emitted by the object being viewed or reflected by the object from a source other than the instrument.
- Active instruments provide their own energy (electromagnetic radiation) to illuminate the object or scene they observe. They send a pulse of energy from the sensor to the object and then receive the radiation that is reflected or backscattered from that object. Scientists use many different types of active remote sensors.
Remote sensing contributes to scientific knowledge by providing valuable information about the Earth’s surface. This includes data on location, depth, biomass, temperature, moisture content, and more. Researchers can use this information to understand various environmental processes better.
Geographic Information Science and Remote Sensing emphasizes using geospatial technology to analyze the spatial interactions among natural and social forces at multiple scales across the Earth’s surface, and exploring the impacts of using such technology on social and cultural interactions.
Geographers use a variety of remote sensing techniques, measuring various types of energy, to study Earth’s atmosphere, hydrosphere, lithosphere, and biosphere.
So the data is stored in rows and columns. Because PostGIS is a spatial database, the data also has a geometry column with data in a specific coordinate system defined by spatial reference identifier (SRID).
Schemas are like folders, and can hold tables, views, functions, sequences and other relations. Every database starts out with one schema, the public schema.
Including all geometry information allows PostGIS to use EWKB as the format of record (e.g. in DUMP files). EWKB and EWKT are used for the “canonical forms” of PostGIS data objects. For input, the canonical form for binary data is EWKB, and for text data either EWKB or EWKT is accepted.
It turns out that PostGIS geometries are limited by the 1 GB limit. PostGIS stores all coordinates at double precision, so we need 16 bytes of storage space per vertex for a 2D geometries (24 bytes for a 3D geometry) in addition to the overhead of the geometry’s headers.
PostGIS is an open source, freely available spatial database extender for the PostgreSQL Database Management System (a.k.a DBMS).