5.3. The Indian Remote Sensing (IRS) satellite

India’s first civilian remote sensing satellite IRS-1A was launched in March 1988. The first generation satellites IRS-1A and -1B were designed, developed and launched successfully during 1988 and 1991 with multispectral cameras LISS-I (Linear Imaging and Self Scanning sensor) and LISS-II at spatial resolutions of 72.5 m and 36.25 m, respectively.

The Indian Remote Sensing (IRS) program began with the launch of IRS-1A in 1988, marking India's entry into satellite-based earth observation. IRS-1A and its successor IRS-1B were equipped with sophisticated multispectral cameras known as LISS-I and LISS-II. These cameras allowed for the capture of images at two different resolutions: 72.5 meters and 36.25 meters. This means that every pixel in the image corresponds to an area of 72.5 meters by 72.5 meters for LISS-I and 36.25 meters by 36.25 meters for LISS-II, providing valuable data for various applications.

Think of these satellites as cameras that take pictures of the Earth from space. Just as a photographer might choose different lenses or settings depending on the subject, like flowers or landscapes, these satellites use different sensors to capture detailed images of land, crops, and urban areas, helping farmers, urban planners, and scientists monitor changes on the Earth.

It was launched in a sun-synchronous orbit, at a nominal altitude of 904 km. It had an orbital period of 103.2 minutes with a repeat cycle of 22 days, crossing the equator around 10:26 AM.

The IRS satellites operate in what's called a sun-synchronous orbit, which means they pass over the same location on Earth at the same local solar time. This helps ensure consistent lighting conditions for the images taken. At an altitude of about 904 km, they complete an orbit every 103.2 minutes and have a repeat cycle of 22 days. This means after 22 days, the satellite will be in the same position over the Earth again, allowing for repeated observations of the same area.

Imagine a train that circles a city every hour. If you want to see how the city changes every week, you would need to take pictures of it at the same time each hour, waiting for the train to come back. The IRS satellites do something similar, ensuring their images are always taken at the same time of day for reliable comparisons.

The IRS-1A and -1B carried LISS-I and -II; each with a multispectral camera providing images in 4 bands (0.46-0.52 µm blue, 0.52-0.59 µm green, 0.62-0.68 µm red, and 0.77-0.86 µm NIR) at 7 bits radiometric resolution.

The LISS-I and LISS-II cameras onboard the IRS satellites were equipped to capture images across four specific spectral bands: blue, green, red, and near-infrared (NIR). Each band corresponds to a different part of the light spectrum, which helps in identifying various land features. The radiometric resolution of 7 bits means that the satellites can capture 128 different shades for each pixel in the images, allowing for detailed analysis of colors and textures.

Consider a painter using four different colors to create a landscape. Each time they paint using a different color, they can represent various aspects of the scene, like the blue sky, green grass, rich brown soil, and the vibrant green vegetation. Similarly, the IRS satellites use these color bands to create a detailed picture of the Earth, helping scientists analyze everything from vegetation health to water bodies.

The second generation satellites, IRS-1C and -1D with improved spatial resolutions have been successfully launched in 1995 and 1997, respectively.

The IRS-1C and -1D satellites were the second generation of the IRS program, launched in 1995 and 1997. These satellites included upgraded sensors for better spatial resolution, allowing them to capture more detailed images of the Earth's surface. The improved technology aimed at enhancing the capabilities for applications such as resource management and environmental monitoring.

Think of upgrading from a standard smartphone camera to a high-resolution DSLR camera. The newer camera captures sharper images with more detail, which is crucial for professional photography. Similarly, the second generation IRS satellites gave researchers and policymakers higher quality images for making informed decisions about land use, agriculture, and monitoring the environment.

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