Tag: weather forecasting

Reading fog data from INSAT 3DR

At 7.57 am today, the India Meteorological Department’s Twitter handle posted this lovely image of fog over North India on January 21, as captured by the INSAT 3DR satellite. However, it didn’t bother explaining what the colours meant or how the satellite captured this information. So I dug a little.

At the bottom right of the image is a useful clue: “Night Microphysics”. According to this paper, the INSAT 3D satellite has an RGB (red, green, blue) imager whose colours are determined by two factors: solar reflectance and brightness temperature. Solar reflectance is a ratio of the amount of solar energy reflected by a surface and the amount of solar energy incident on it. Brightness temperature has to do with the relationship between the temperature of an object and the corresponding brightness of its surface. It is different from temperature as we usually understand it – by touching a glass of hot tea, say – because brightness temperature also has to do with how the tea glass emits the thermal radiation: at different frequencies in different directions.

INSAT 3D’s ‘day microphysics’ data component studies solar reflectance at three wavelengths: 0.5 µm (visible), 1.6 µm (shortwave infrared) and 10.8 µm (thermal infrared). The strength of the visible signal determines the amount of green colour; the strength of the shortwave infrared signal, the amount of red colour; and the strength of the thermal infrared signal, the amount of blue colour. This way, the INSAT 3D computer determines the colour on each point of the screen.

‘CB’ stands for ‘cumulonimbus’

According to the paper:

The major applications of this colour scheme are an analysis of different cloud types, initial stages of convection, maturing stages of a thunderstorm, identification of snow area and the detection of fires.

The authors also note that the INSAT 3D is useful to image snow: while the solar reflectance of snow and the clouds is similar in the visible part of the spectrum, snow absorbs radiation of 1.6 µm strongly. As a result, when the satellite is imaging snow, the red component of the colour scheme becomes very weak.

The night microphysics is a little more involved. Here, two colours are determined not by a single signal but by the strength of the difference between two signals. The computer determines the amount of red colour according to the difference between two thermal infrared signals: 12 µm and 10 µm. The amount of green colour varies according to the difference between a thermal infrared and a middle infrared signal: 10.8 µm and 3.9 µm. The amount of blue colour is not a difference but is determined by the strength of a thermal infrared signal of wavelength 10.8 µm.

For example, in the image above, the data indicates three kinds of clouds. (‘K’ denotes the temperature differences in kelvin.) A mature cumulonimbus cell, possibly part of a tropical storm, hangs over West Bengal and is visible mostly in red, but whose blue component indicates it is also very cold. Somewhere north of Delhi, flecks of green dominate, indicating a preponderance of lower clouds. Further north, a the sky is dominated by a heavy, high cloud system that encompasses lower clouds as well.

By combining day and night microphysics data, atmospheric scientists can elucidate the presence of moisture droplets of different shapes and temperature differences over time, and in turn track the formation, evolution and depletion of cyclones and other weather events.

For example, taking advantage of the fact that INSAT 3D can produce images based on signals of multiple wavelengths, the authors of the paper have proposed day and night microphysics data that they say would indicate a thunderstorm impending in one to three hours.

Both INSAT 3D and INSAT 3DR use radiometers to make their spectral measurements. A radiometer is a device that measures various useful properties of radiation, typically by taking advantage of radiation’s interaction with matter (e.g. in the form of temperature or electrical activity).

Both satellites also carry atmospheric sounders. They measure temperature and humidity and study water vapour as a function of their heights from the ground.

Scientists combine the radiometer and sounder measurements to understand various atmospheric characteristics.

According to the INSAT 3DR brochure, its radiometer is an upgraded version of the very-high-resolution radiometer (VHRR) that the Kalpana 1 and INSAT 3A satellites used (launched in 2002 and 2003, respectively).

The Space Application Centre’s brief for INSAT 3A states: “For meteorological observation, INSAT-3A carries a three channel Very High Resolution Radiometer (VHRR) with 2 km resolution in the visible band and 8 km resolution in thermal infrared and water vapour bands.” The radiometers onboard 3D and 3DR have “significant improvements in spatial resolution, number of spectral channels and functionality”.

The Kalpana 1 and INSATs 3A, 3D and 3DR satellites aided India’s weather monitoring and warning services with the best technology available in the country at the time, and with each new satellite being an improved as well as better-equipped version of the previous one. So while Kalpana 1 had a launch mass of 1,060 kg and carried a early VHRR and a data-relay transponder, INSAT 3DR had a launch mass of 2,211 kg – in 2016 – and carried an upgraded VHRR, a sounder, a data-relay transponder and a search-and-rescue transponder.

India deactivated Kalpana 1 in September 2017, after 15 years in orbit. The INSAT 3A, 3D and 3DR satellites are currently active in a geostationary orbit around Earth, at inclinations respectively of 93.5º, 82º and 74º E longitudes.

Cybersecurity in space

Featured image: The International Space Station, 2011. Credit: gsfc/Flickr, CC BY 2.0

On May 19, 1998, the Galaxy IV satellite shut down unexpectedly in its geostationary orbit. Immediately, most of the pagers in the US stopped working even as the Reuters, CBS and NPR news channels struggled to stay online. The satellite was declared dead a day later but it was many days before the disrupted services could be restored. The problem was found to be an electrical short-circuit onboard.

The effects of a single satellite going offline are such. What if they could be shutdown en masse? The much-discussed consequences would be terrible, which is why satellite manufacturers and operators are constantly devising new safeguards against potential threats.

However, the pace of technological advancements, together with the proliferation of the autonomous channels through which satellites operate, has ensured that operators are constantly but only playing catch-up. There’s no broader vision guiding how affected parties could respond to rapidly evolving threats, especially in a way that constantly protects the interests of stakeholders across borders.

With the advent of low-cost launch options, including from agencies like ISRO, since the 1990s, the use of satellites to prop up critical national infrastructure – including becoming part of the infrastructure themselves – stopped being the exclusive demesne of developed nations. But at the same time, the drop in costs signalled that the future of satellite operations might rest with commercial operators, leaving them to deal with technological capabilities that until then were being handled solely by the defence industry and its attendant legislative controls.

Today, satellites are used for four broad purposes: Earth-observation, meteorology and weather-forecasting; navigation and synchronisation; scientific research and education; and telecommunication. They’ve all contributed to a burgeoning of opportunities on the ground. But in terms of their own security, they’ve become a bloated balloon waiting for the slightest prick to deflate.

How did this happen?

Earlier in September, three Chinese engineers were able to hack into two Tesla electric-cars from 19 km away. They were able to move the seats and mirrors and, worse, control the brakes. Fortunately, it was a controlled hack conducted with Tesla’s cooperation and after which the engineers reported the vulnerabilities they’d found to Tesla.

The white-hat attack demonstrated a paradigm: that physical access to an internet-enabled object was no longer necessary to mess with it. Its corollary was that physical separation between an attacker and the target no longer guaranteed safety. In this sense, satellites occupy the pinnacle of our thinking about the inadequacy of physical separation; we tend to leave them out of discussions on safety because satellites are so far away.

It’s in recognition of this paradigm that we need to formulate a multilateral response that ensures minimal service disruption and the protection of stakeholder interests at all times in the event of an attack, according to a new report published by Chatham House. It suggests:

Development of a flexible, multilateral space and cybersecurity regime is urgently required. International cooperation will be crucial, but highly regulated action led by government or similar institutions is likely to be too slow to enable an effective response to space-based cyberthreats. Instead, a lightly regulated approach developing industry-led standards, particularly on collaboration, risk assessment, knowledge exchange and innovation, will better promote agility and effective threat responses.

Then again, how much cybersecurity do satellites need really?

Because when we speak about cyber anything, our thoughts hardly venture out to include our space-borne assets. When we speak about cyber-warfare, we imagine some hackers at their laptops targeting servers on some other part of the world – but a part of the world, surely, and not a place floating above it. However, given how satellites are becoming space-borne proxies for state authority, they do need to be treated as significant space-borne liabilities as well. There’s even precedence: In November 2014, an NOAA satellite was hacked by Chinese actors with minor consequences. But in the process, the attack revealed major vulnerabilities that the NOAA rushed to patch.

So the better question would be: What kinds of protection do satellites need against cyber-threats? To begin with, hackers have been able to jam communications and replace legitimate signals with false ones (called spoofing). They’ve also been able to invade satellites’ SCADA systems, introduce viruses to trip up software and,  pull DOS attacks. The introduction of micro- and nanosatellites has also provided hackers with an easier conduit into larger networks.

Another kind of protection that could be useful is from the unavoidable tardiness with which governments and international coalitions react to cyber-warfare, often due to over-regulation. The report states, “Too centralised an approach would give the illicit actors, who are generally unencumbered by process or legislative frameworks, an unassailable advantage simply because their response and decision-making time is more flexible and faster than that of their legitimate opponents.”

Do read the full report for an interesting discussion of the role cybersecurity plays in the satellite services sector. It’s worth your time.