At present, one of the most powerful instruments for the study of climate change ecology, land use land cover changes, ocean temperature, and salinity, and forest application is satellite remote sensing, which measures the flow of radiation entering and exiting the upper atmosphere.
After 1962, the term “remote sensing” became popularized, and it typically refers to nonintrusive Earth observation using electromagnetic waves from a platform some distance away from the object of inquiry. After more than five decades of research and development, humanity can today employ many types of optical and microwave sensors to collect enormous datasets with great accuracy and resolution for the atmosphere, ocean, and land.
Passive Remote Rensing General Overview
Remote sensors can be active or passive. Passive sensors react to outside stimuli (generally a natural source of energy). They measure natural energy reflected or emitted by the Earth’s surface. (The Basic Concept of Remote Sensing) Reflected sunlight is the most prevalent source of radiation measured by passive sensors. Example of passive remote sensing sensors are photographic Cameras, Cross -Track Scanners, Along-Track (Push-Broom) Scanners, Video Cameras, and Microwave Radiometers etc.
Active Remote Sensing General Overview
a sensor that broadcasts a directed pattern of energy to illuminate a portion of the Earth’s surface, then receives the portion scattered back to the instrument. This energy forms the basis for the imagery we interpret. Active sensors generate their own energy, so their use is subject to fewer constraints, and they can be used under a wider range of operational conditions. Example of active sensors is radar, sonar and lidar.
History of Landsat satellite series
The Landsat series is the longest running series of satellites f moderate-resolution optical remote sensing for land, coastal areas and shallow waters. It is a cooperative USGS and NASA Earth Observation program. The first satellite of Landsat mission series was launched in 1972, and also the first Earth Observation satellite with the main objective to monitor the ground surface. It was after followed by successors, however the Landsat 6 satellite failed to reach orbit and communication with the satellite was never established. Recently Landsat 9 was launched in 27 September 2021. Following given table shows the characteristics of all Landsat satellites.
| Satellite | Time period |
| Landsat 1 | July 1972 – 1978 January |
| Landsat 2 | January 1975 – July 1983 |
| Landsat 3 | March 1978 – September 1983 |
| Landsat 4 | July 1982 – December 1993 |
| Landsat 5 | March 1984 – January 2013 |
| Landsat 6 | October 1993 (failure) |
| Landsat 7 | April 1999 (ongoing) |
| Landsat 8 | February 2013 (ongoing) |
| Landsat 9 | September 2021 |
Following figure represents the major application areas of Landsat satellites. It is the series of satellites which provide temporal data from 1972 to present time for the researchers.
Landsat 9
The 9th satellite of Landsat satellite series launched on 27th of September 2021, from Vandenberg Air Force Base, California, onboard a United Launch Alliance Atlas V 401 rocket. it was the most advanced satellite of Landsat series. Data for the public access will be provided from early 2022. It is a joint program between NASA and the US geological survey for the objective of monitoring, mapping, understanding the earth resources in better way. It is a moderate spatial resolution satellite with carrying a pan band. The detail of the bands used in the Landsat 9 is following.
NASA and USGS are responsible for the space segment and ground segment application respectively. The works under space segment procedure include mission integration, launch, and on-orbit checkout. NASA-managed satellite builds have a mission lifecycle (see the image below) that is divided into incremental phases and the case of ground segment the works includes flight operations, data processing, and data product distribution after NASA completes on-orbit checkout.
| Band | Type | EMS Range | Spatial Resolution | Applications |
| 1 | Visible coastal aerosol | (0.43 – 0.45 µm) | 30m | Coastal and aerosol studies |
| 2 | Visible Blue | (0.450 – 0.51 µm) | 30m | Bathymetric mapping, distinguishing soil from vegetation and deciduous from coniferous vegetation |
| 3 | Visible Green | (0.53 – 0.59 µm) | 30m | Emphasizes peak vegetation, which is useful for assessing plant vigor |
| 4 | Visible Red | (0.64 – 0.67 µm) | 30m | Discriminates vegetation slopes |
| 5 | NIR (Near infrared) | (0.85 – 0.88 µm) | 30m | Emphasizes biomass content and shorelines |
| 6 | SWIR (Short wave infrared) | (1.57 – 1.65 µm) | 30m | Discriminates moisture content of soil and vegetation; penetrates thin clouds |
| 7 | SWIR (Short wave infrared) 2 | (2.11 – 2.29 µm) | 30m | Improved moisture content of soil and vegetation; penetrates thin clouds |
| 8 | Panchromatic | (0.50 – 0.68 µm) | 15m | Image sharpness |
| 9 | Cirrus | (1.36 – 1.38 µm) | 30m | Improved detection of cirrus cloud contamination |
| 10 | TIRS 1 (Thermal Infrared) | (10.6 – 11.19 µm) | 100m | thermal mapping and estimated soil moisture |
| 11 | TIRS 2 (Thermal Infrared) | (11.5 – 12.51 µm) | 100m | improved thermal mapping and estimated soil moisture |
Note:- For understanding the better about the importance of TIRS sensor also visit to (Remote Sensing of the Thermal Infrared Spectrum Range)
Landsat 9 spacecraft and Launch Components
- Spacecraft Provider: Northrop Grumman
- Spacecraft Bus: Northrop Grumman Innovation Systems (formerly Orbital ATK).
- Launch Vehicle: United Launch Alliance Atlas V 401.
- Spacecraft Speed: 16,760 miles/hr (26,972 km/hr).
- Design Life: 5 years.
- Consumables: 10 years.
Resolutions of Landsat 9 Satellite
| Type of resolution | Characteristic |
| Spatial resolution | 30m (visible, NIR, and SWIR bands), 15m (Pan) and 100m (TIRS) [Table 1] |
| Temporal Resolution | 16 days (8-day offset with Landsat 8) |
| Radiometric Resolution | 14-bit quantization increased from 12 bits for Landsat 8 |
How to Access Landsat Series Data Sets
For accessing the Landsat satellite series data sets USGS develop a web based platform of earth explorer (EarthExplorer) and Google earth engine. Earth explorer is the official website for collecting the satellite data of Landsat as well as several others such as Modis, Sentinal, NASA’s processed datasets (NASA LPDAAC Collection), SRTM digital elevation data etc.
A Users can navigate via interactive map or text search to obtain Landsat satellite imagery, Radar data, UAS data, digital line graphs, digital elevation model data, aerial photos, Sentinel satellite data, some commercial satellite imagery including IKONOS and OrbView3, land cover data, digital map data from the National Map, and many other datasets. The required datasets can be search by exact location via the interactive map or input specific coordinates to view what data types are available.
