Indian Climate Observatory Network (ICON) Tower - Gadanki Indian Climate Observatory Network (ICON) is an initiative of NARL to generate high quality long-term data set for climate search. First observatory of this network is established at NARL, Gadanki with following facilities to measure aerosols, trace-gases and radiation. Radiation and Remote Sensing Sky-Radiometer (seven wavelengths) Pyranometer (three sensors) Pyrheliometer Total Sky-imager LIDAR

In-situ aerosol Instruments Aethalometer Nephelometer Aerodynamic particle size Analyzer Fine-particulate sampler In-situ trace gaces measurements O3 Analyser NOx Analyser SO2 Analyser CO Analyser CO2 Analyse Sky-Radiometer Prede Skyradiometer (Prede Co. Ltd., Tokyo, Japan) is an instrument to measure direct solar radiation and directional sky radiation with respect to sun position. The instrument has automatic sun-tracker and filter wheel with seven filters namely 315 nm, 400 nm, 500 nm, 675 nm, 870 nm, 940 nm and 1020 nm. The rain sensor helps instrument stop taking reading and point downward during rain in order to avoid rain drop getting on lens of instrument. The instrument is used to get aerosol optical depth at five wavelengths, columnar aerosol size distribution, columnar single scattering albedo, columnar average refractive index of aerosols and columnar water vapour.

Pyranometer & Pyrheliometer Kipp and Zonen pyranometer with automatic sun-tracker and four sensors is used to measure broadband surface reaching solar radiation. Two of these sensors are used to get diffuse flux whereas one for total (direct+diffuse) and one for direct solar radiation.

Total Sky Imager Total sky imager is an instrument which records true color RBG images of hemispherical sky. The images are recorded at every five minutes during daylight hours. An image processing software estimates the cloud fraction from this image.

Nephelometer Scattering coefficient is measured using integrating nephelometer (Model: TSI 3563) at NARL. Nephelometer gives hemispherical total (integrated between 7 to 170 degree) and back (integrated between 90 to 170 degree) scattering coefficient at three wavelengths 450 nm, 550 nm and 700 nm. The actual measurement of this instrument is the photons scattered by sampling air. Nephelometer, Aerodynamic Particle Sizer and Athelometer at ICON observatory Relevant calibration constants are used to convert the measured photon counts into corresponding scattering coefficient. Once in every one hour sampling air is filtered for aerosol to obtain scattering due to clear air, which is subtracted from sample air to get scattering due to aerosol. Calibration constants are determined by using CO2 gas at approximately every six months.The instrument is continuously operated day and night since Oct 2008 and data are saved as five minutes averages.

Aethalometer Aethalometer (Model AE-31E; Magee Scientific Company) is a self-contained, automatic instrument which measures mass concentration of 'Black' or 'Elemental' carbon particles ('BC' or 'EC') in ambient air. In the aethalometer, ambient air is drawn through an inlet port at a flow rate of few litres per minute using a small internal pump. It collects the sample as a spot on a roll of quartz fibre filter tape and simultaneously measures the optical attenuation of the collected sample at seven different wavelengths ranging from 370 nm to 950 nm. The measured attenuation at a given wavelength is linearly related to concentration of BC on the tape. It gives continuous reading at an interval selectable by user (typically 5 minutes).

Aerodynamic Particle Sizer: Aerodynamic Particle Sizer (Model : 3321, TSI Inc, USA) abbreviated as APS is used to measure the surface aerosol number size distribution in 52 bins for aerodynamic diameter ranging from 0.5 µm to 19.8 µm. It uses the time of flight technique for estimating the aerodynamic particle diameter in the real time. The ambient air is drawn through an inlet port at a flow rate of 5 litre per minute using internal pumps. The instrument is operated with time resolution of 5 minutes since October 2008 from ICON observatory.

Lidar for Atmospheric Measurement and Probing [LAMP]: LAMP is a single channel mono-static coaxial LIDAR (LIght Detection And Ranging) which works on the principle of elastic scattering of radiation. It provides valuable information about the distribution of aerosols and clouds in the atmosphere during night-time. It mainly consists of a diode-pumped Nd:YAG Laser (transmitter), which emits laser pulses of pulse energy between 1-25 µJ at a wavelength of 532 nm with a pulse-repetition rate of 2.5 kHz, a 150 mm diameter Cassegrain type telescope (receiver) for collecting the back-scattered photons from the atmospheric scatterers (like air molecules, aerosols and cloud particles) and a photon-counting system (photomultiplier tube, discriminator and a PC based multi-channel scalar). The laser photons are transmitted into the atmosphere, they suffer scattering with the atmospheric scatterers in all directions within the beam. A part of these scattered photons are collected by the telescope in the backward direction and are counted by the photo-multiplier tube. The time of flight of the scattered photon gives the range of the scatterer from the telescope. These range-resolved photons counts are used to obtain various optical properties of aerosols and cloud layers viz. back-scattering coefficient, extinction coefficient, optical thickness, cloud base and top height, cloud optical thickness etc. This system is developed in NARL and patented under ISRO. This system is operated from ICON since October 2010 every night except weekends.