An Advanced Radiosonde System for Aerospace Applications

An Advanced Radiosonde System for Aerospace Applications

U. S. DIVYA, J. GIRIJA, S. SATYANARAYANA,* AND JOHN P. ZACHARIAH

Avionics Entity, Vikram Sarabhai Space Centre, Thiruvananthapuram, Kerala, India

(Manuscript received 31 January 2013, in final form 29 March 2014)

ABSTRACT

The Indian Space Research Organization (ISRO)’s Vikram Sarabhai Space Centre (VSSC) has developed

a new GPS radiosonde, called Pisharoty sonde, with its ground station for atmospheric research and opera-

tional meteorology. The latest version of this radiosonde weighs 125 g and uses a bead thermistor, a capacitive

humidity sensor, and a GPS receiver module. It computes geopotential heights and pressures using the

temperature and GPS altitude profile. This paper describes the radiosonde and its associated ground system,

summarizes its different versions, and discusses balloon tests of the newly developed version, including

comparisons with internationally accepted high-quality radiosondes.

1. Introduction

The Indian Space Research Organization (ISRO)’s

Vikram Sarabhai Space Centre (VSSC) has developed a

new, low-costGPS radiosonde system called the Pisharoty

sonde system. It is named after P.R. Pisharoty, the famous

Indian physicist and meteorologist who founded the In-

dian Institute of Tropical Meteorology. To meet ISRO

requirements for detailed profiles, especially in the lower

troposphere, simple operation, light weight, and low cost,

the current operational Pisharoty sonde (weighing 125 g,

including batteries) has a single electronics board, a bead

thermistor, a capacitive relative humidity (RH) sensor,

and a GPS module to obtain height and wind data. Pres-

sure is computed hydrostatically. The system provides

detailed lower-troposphere profiles at a lesser cost than its

available counterparts in the international market. The

Pisharoty sonde system supports all ISRO space launch

activities and atmospheric research programs. It is also

used by agencies like the India Meteorological De-

partment (IMD) and universities for their meteorological

studies. The technology developed by ISRO-VSSC

is transferred to another ISRO center, Semi-Conductor

Laboratories (SCL) in Chandigarh, for manufacturing the

sondes. The following sections summarize the latest ver-

sion of the radiosonde, the ground station and data

processing, different versions, validation, and special ap-

plications.

2. System configuration

The Pisharoty sonde system consists of two sub-

systems, namely, the sonde and the ground station.

Figure 1 gives a schematic representation of the Pisharoty

sonde system.

a. Pisharoty sonde

The sonde consists of sensors for measuring tempera-

ture and relative humidity; a sigma delta analog-to-digital

converter (ADC) to process sensor data; a GPS module

to get the navigation parameters; a microcontroller for

initialization, data acquisition, and frame formatting;

a transmitter module for carrier generation, modulation,

and transmission; an antenna; and a battery.

A photograph of the sonde is given in Fig. 2a and the

block diagram in Fig. 2d. The temperature and RH

sensor are mounted outside the sonde package on

a flexible printed circuit board (PCB), but the batteries

and other electronic parts are inside the insulated ra-

diosonde case.

Pressure is calculated from temperature and geo-

potential height using software in the data processing and

display system of the ground station. The temperature

*Retired.

Corresponding author address: U. S. Divya, RF Advanced

Technology Division, Avionics Entity, Vikram Sarabhai Space

Centre, Veli, ISRO Post, Thiruvananthapuram 695022, Kerala,

India.

E-mail: [email protected]; [email protected]; john_zachariah@

vssc.gov.in

OCTOBER 2014 D IVYA ET AL . 2067

DOI: 10.1175/JTECH-D-13-00050.1

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mailto:[email protected]




sensor is a negative temperature coefficient glass bead

thermistor with a base resistance of 1 kV at 258C (0.4-

mm diameter and without antiradiation coating). The

humidity sensor gives an output voltage proportional to

the relative humidity (sensor module of 8mm 3 4mm 33mm covered by an aluminized plastic cap of 15-mm

diameter). The voltage outputs from the sensor circuits

are collected and processed by the sigma delta ADC

sequentially.

The GPS receiver module with an integrated patch

antenna gives altitude, time, location, and velocity of

the balloon by processing the signals from GPS satel-

lites. The output from the GPS receiver is in National

Marine Electronics Association (NMEA) standard mes-

sages format.

The microcontroller acquires the data from ADC and

GPS, multiplexes the data, and applies error correction

coding. Reed–Solomon coding, being best suited for

systems prone to burst errors, is used in the sonde system

for forward error correction. The telemetry frame with

a frame synchronization pattern, multiplexed data, and

error coding bytes are fed to the transmission block.

Telemetry data are frequency-shift keying (FSK) mod-

ulated on a carrier with frequency programmability in

the range of 402–406MHz.

Acquisition, processing, and transmitting electronics,

based on commercial off-the-shelf (COTS) components

operating at 3.3V or less, are placed on a single elec-

tronic board. Including two AA lithium-thionyl chloride

batteries (allowing for operation for more than 4 h), the

radiosonde weighs 125 g. Sensor calibration coefficients

are stored on chip, and the preparation and initialization

procedure takes less than 5 min. Initialization includes

programming the transmission frequency to any desired

125-kHz step between 402 and 406MHz.

The bead thermistor is subject to radiation errors,

including heating by sunlight and cooling by radiation to

space, as well as a lag in responding to temperature

changes as the balloon ascends, with all errors being

larger at high altitudes. A solar and IR radiation cor-

rection, varying with pressure and sun angle, is applied

to compensate for all of these errors. The correction

table was derived using comparison flights described in

section 3b. For example, at 50 hPa the correction is

22.58C (the reported temperature is reduced) at high

sun angles and 10.68C at night. While the RH sensor is

similarly subject to errors, the RH data are currently not

adjusted.

The activities for bulk production of the latest version

of the sondes were initiated after building up confidence

with sufficient trial and comparison ascents, and this

version of the system is planned to be operational by

mid-2014.

b. Ground station

The ground station consists of three main systems:

(i) antennas and low noise blocks (LNBs), (ii) a Pisharoty

sonde receiver, and (iii) a data processing and display

system.

For full hemispherical coverage and high-quality signal

reception, two independent antennas [amonopole antenna

and a quadrifilar helix (QFH) antenna] are used for re-

ceiving signals radiated from the sonde. The output of each

antenna is fed to the respective LNB,which contains a low-

noise amplifier (LNA) and a narrow bandpass filter (BPF).

The LNA gives sufficient amplification to the received

signal to compensate the signal attenuation due to cable

loss. A picture of the antenna assembly is shown in Fig. 2b.

The Pisharoty sonde dual-channel FSK receiver ac-

cepts signals from both the antennas simultaneously,

demodulates, decodes independently, and sends the

data from both the channels to the data processing and

display system. The dual-channel receiver system with

high sensitivity and Reed–Solomon decoding ensures a

good telemetry link (even up to a range of 300 km), and

the data loss is less than 0.2% (i.e., fewer than 12 frames

out of a total of 6000 frames) in the high-resolution 1-s

FIG. 1. Schematic representation of the Pisharoty sonde system.

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data file for most of the cases. Error detection schemes,

including checksum verification, ensure good-quality

data throughout the ascent.

The data processing and display system, developed by

ISRO and called Indian Radiosonde Software (IndRoS),

is installed on either a Windows XP, Windows-7, or

Windows-8 desktop, or a laptop computer with Ethernet

interface for Transmission Control Protocol/Internet

Protocol (TCP/IP) connectivity to connect to the receiver

for data collection or system configuration.

A photograph of the receiver and the data processing

and display system is shown in Fig. 2c, and the block

diagram is given in Fig. 2e.

3. Development and testing

a. Pisharoty sonde versions

ISRO-VSSC initiated the development of radio-

sondes in 2005. In 2006, prototype Pisharoty sonde

was first flown from the Tata Institute of Fundamen-

tal Research (TIFR) Balloon Facility at Hyderabad

and data was received using a prototype sonde re-

ceiver. This sonde prototype model had a platinum

resistance temperature detector (RTD), a microelec-

tromechanical systems (MEMS) pressure sensor,

and a GPS receiver module for acquiring various

parameters.

FIG. 2. Photographs of (a) Pisharoty sonde, (b) antenna with LNBs in radome, and (c) Pisharoty sonde receiver and data processing and

display system. Block diagrams of (d) Pisharoty sonde and (e) ground station.



The first operational version of the system includes

the PS01_A1 Pisharoty sonde, with similar sensors and

GPS receiver as the prototype, a capacitive humidity

sensor, a modified data acquisition module, and an

upgraded transmitter. Also, the ground system, including

the signal acquisition antennas and the data processing

software, was further improved. However, this version

had no on-chip coefficient storage, no frequency pro-

grammability as part of initialization, and no temperature

or humidity radiation correction. This system was tested

by radiosonde releases from the Vikram Sarabhi Space

Centre at Thumba (WMO station 43373) and the ocean

Research Vessel Sagar Kanya (call sign VTJR) between

September 2008 andOctober 2010 (Bala Subrahamanyam

et al. 2012; Bala Subrahamanyam and Anurose 2011;

Anurose et al. 2012; Rao 2008).

Highly accurate pressure sensors capable of working

at low temperatures make the sondes heavy and costly.

The second operational version of the Pisharoty sonde

(PS01_B2) is used routinely at Thumba and in various

Indian research programs starting in late 2011. It adopts

the software approach to compute pressure using the

temperature profile and geopotential height, which is

calculated accurately from the geometric height obtained

fromGPS (Nash et al. 2011). The PS01_A1 and PS01_B2

sensors are identical (although the temperature–humidity

sensor PCB is modified), but the data processing and

display software allows the user to select pressure data

either from the software or from the pressure sensor.

The PS01_B2 software also corrects temperature read-

ings to minimize solar radiation errors (corrections were

derived from comparison flights with imported radio-

sondes in mid-2011). Other modifications in sonde, re-

ceiver, and software incorporate features like frequency

programmability and onboard coefficient storage.

The first two operational versions of the Pisharoty

sondes had a platinum wire RTD as a temperature

sensor, but because of large radiative heating errors, the

third (latest) operational version (PS01_B3) of sondes

was developed with a very small glass bead thermistor as

a temperature sensor (custom made for VSSC), with

solar and infrared radiation corrections in ground soft-

ware. The pressure sensor is omitted and pressure is

computed in ground software. Development and vali-

dation of this system has been completed, and the results

are discussed in detail in the following section. Specifi-

cations of this latest version of sonde are given in Table 1.

These are 2s values (95.5% of the errors in the mea-

surements are within the listed values).

Throughout the development process, the Pisharoty

sonde ground station has also improved significantly, of

which the major milestones were the antenna design,

development of a dual-channel receive chain, the

implementation of coding schemes, and modifications in

processing software to make it fault tolerant. De-

velopment of the receiver system is not discussed in detail

because the ground system changes have little effect on

the output data biases.

b. Comparisons and operational testing

The latest version (PS01_B3) of Pisharoty sonde (with

bead thermistor, and computed pressure, as there is no

pressure sensor) was validated by comparison ascents,

where the Pisharoty sonde and another radiosonde

(Vaisala, Meisei, or Graw) were attached to a 1.5-m

stick suspended in a horizontal plane by a 30-m string

below the balloon. The balloon was inflated in such

a way that the mean ascent rate is 5m s21. Comparison

ascents with Vaisala RS92-SGPD were conducted at

IMD in New Delhi (WMO station 42182, 5 flights from

10 to 13 December 2010), with Graw DFM-06 radio-

sondes at Kochi Naval Base (WMO station 43353, 4

flights from 27 to 29 January 2011), and with Meisei

RS-06G at the National Atmospheric Research Labo-

ratory (NARL) in Gadanki (10 flights from 21 to 23 July

2011). Ascents were performed every few hours to val-

idate system performance during the entire diurnal

cycle. Comparisons in Table 2 and Figs. 3–7 include ra-

diation corrections on temperature data, and each dif-

ference is the PS01_B3 Pisharoty sonde reading minus

the other sonde reading.

Comparison plots are generated as follows:

1) Pisharoty sonde raw data are available at a 1-Hz

rate and vertical profiles of wind parameters are

smoothed through a 61-point moving averaging

technique to compensate for the disturbances,

including balloon oscillations. A total of 15 consec-

utive points are averaged for temperature, pressure,

and RH.

2) Since the data from Vaisala are available once every

2 s and data from Graw and Meisei are available

TABLE 1. Specifications of the Pisharoty sonde.

Temperature Range 2908 to 608CResolution 0.18CAccuracy 618CResponse time ,1 s

Pressure Accuracy 61.4 hPa (.100 hPa)

60.5 hPa (#100 hPa)

Relative humidity

(temp . 2408C)Range 0%–100%

Resolution 0.1%

Accuracy 65%

Response time ,5 s

Wind velocity Range 0–500m s21

Resolution 0.01m s21

Accuracy 0.1m s21



every second, data points for comparison are taken at

4-s intervals (i.e., points corresponding to time count

1, 5, 9, etc.), which provides sufficiently high-

resolution data. If any of these points are not avail-

able (a missing point), then linear interpolation is

done, provided an adjacent point is available within

4 s. Otherwise, the data point is treated as a missing

point in the 4-s interval profile and is not considered

for error computation.

3) Differences between the corresponding values of two

sondes for various parameters are calculated.

4) Before plotting, a 61-point moving averaging is done

on differences in the 4-s interval vertical profile to

remove random noises.

Typical comparison plots of the Pisharoty sonde with

Vaisala and Meisei are shown in Figs. 3–6 (temperature,

pressure, humidity, and wind speed and direction, re-

spectively). In Fig. 4, computed Pisharoty sonde pressures

are compared with that of Vaisala. For RH, Pisharoty

sonde RH is compared only until the temperature drops

below2408C. In all plots, the time count is the number of

TABLE 2. Correlation of the Pisharoty sondes with other radiosondes.

Parameter Sonde Time

No. of

ascents

No. of

points R Std dev Slope Intercept

Temperature Vaisala Day 3 1584 0.999 0.375 0.999 20.003

Night 1 535 0.999 0.517 0.989 20.936

Dusk 1 500 0.999 0.278 0.993 20.174

Meisei Day 3 1610 0.999 0.619 1.003 0.169

Night 3 1077 0.999 0.297 0.994 20.019

Dawn 2 1152 0.999 0.425 0.991 20.114

Dusk 2 1102 0.999 0.474 1.001 0.057

Graw Dawn 2 1387 0.999 0.740 1.008 20.577

Dusk 2 1307 0.999 0.284 1.001 20.222

Pressure Vaisala Day 3 1584 1 0.394 0.997 20.15

Night 1 535 0.999 0.893 0.995 21.179

Dusk 1 500 1 0.336 0.998 20.306

Meisei Day 3 1610 1 0.804 0.995 20.26

Night 3 1077 0.999 0.858 0.996 20.699

Dawn 2 1152 0.999 0.847 0.994 20.381

Dusk 2 1102 0.999 2.4 0.997 20.94

Graw Dawn 2 1387 0.999 1.445 0.996 20.278

Dusk 2 1307 1 0.683 0.999 20.397

Relative humidity Vaisala Day 2 441 0.94 4.22 0.827 5.226

Night 1 207 0.978 2.513 0.918 8.97

Meisei Day 3 585 0.87 7.09 0.77 5.79

Night 1 204 0.889 4.59 0.889 15.51

Dawn 2 411 0.913 6.167 0.979 5.63

Dusk 2 400 0.953 5.005 0.863 12.17

Graw Dawn 1 285 0.988 3.91 1.023 5.068

Dusk 1 251 0.988 4 0.956 5.129

East–west wind Vaisala Day 3 1584 0.999 0.747 0.997 0.102

Night 1 535 0.999 0.856 0.999 20.009

Dusk 1 500 0.999 0.655 0.997 0.056

Meisei Day 3 1600 0.992 2.33 0.964 0.322

Night 3 1077 0.997 1.32 0.984 20.094

Dawn 2 1138 0.996 1.48 0.996 0.434

Dusk 2 1000 0.994 1.92 0.95 20.001

Graw Dawn 2 1387 0.999 0.230 1.029 20.003

Dusk 2 1307 0.999 0.164 1.028 0.029

North–south wind Vaisala Day 3 1584 0.988 0.764 0.962 20.158

Night 1 535 0.977 0.758 0.941 20.504

Dusk 1 500 0.978 0.608 0.916 20.309

Meisei Day 3 1600 0.93 1.58 0.85 0.105

Night 3 1077 0.973 1.355 0.92 0.145

Dawn 2 1138 0.985 0.743 0.948 0.134

Dusk 2 1000 0.959 1.34 0.825 0.478

Graw Dawn 2 1387 0.998 0.248 1.027 0.032

Dusk 2 1307 0.998 0.181 1.025 0.022



seconds after the balloon release. In Figs. 3–6, the differ-

ence is calculated as the Pisharoty sonde data valueminus

the Vaisala or Meisei data value at each level. Launch

times are in Indian standard time (IST), where IST 5UTC 1 5.5 h. Data from other comparison ascents also

have similar differences for the measured parameters.

To analyze the repeatability and accuracy in the per-

formance of the systemwith respect to other sondes used in

comparison ascents, scatterplots combining data from all

the ascents (19 ascents) are generated as described below.

Vertical profiles are smoothed through the moving

averaging technique (61 points for wind parameters and

15 points for temperature, pressure, and RH) to com-

pensate for the disturbances, including balloonoscillations.

Then, scatterplots for different parameters are drawn by

taking the corresponding data points from both the sondes

at 10-s intervals (which provides a sufficiently large num-

ber of points for the statistical analysis). Linear inter-

polation is done to obtain the missing points, provided

a valid data point is available within 10 points from the

missing data.

Scatterplots for various parameters are given in Fig. 7.

‘‘PS01’’ indicates the Pisharoty sonde. Total number of

points (N), correlation (R), and standard deviation (SD)

are found and these values are given in the graphs. A best-

fitting straight line is drawn to study the linearity. The

equation of the best-fit line with slope and intercept is also

indicated in the figure. In 2 (out of 5) ascents with Vaisala,

2 (out of 10) ascents with Meisei, and 2 (out of 4) ascents

with Graw, humidity sensors were not used in Pisharoty

FIG. 3. Plots of the comparison ascents of (a) temperature profiles of Pisharoty sonde and

Vaisala at 1207 IST 11 Dec 2010, (b) corresponding temperature difference. (c),(d) As in (a),

(b), but for comparison with Meisei sonde at 2322 IST 21 Jul 2011.



sondes, as the main intention of these comparison ascents

was the validation of temperature data. So, for these as-

cents RH is not compared. For other ascents, RH is con-

sidered until the temperature drops below 2408C.To further analyze the Pisharoty sonde performance

during the entire diurnal cycle with respect to each of the

imported sondes, ascents are classified into groups and

the correlation with other sondes is found as follows:

1) The entire dataset of comparison ascents is split into

three groups based on the imported sonde used

(Vaisala, Meisei, or Graw).

2) Each of these groups is further divided into subgroups

based on time of ascent (day, night, dawn, or dusk).

3) Scatterplots for different parameters are drawn for

each of these subgroups and a best-fit straight line is

also found. Obtained plots are similar to the com-

bined scatterplot shown in Fig. 7. The total number

of points considered, correlation, standard deviation,

slope, and intercept of all parameters for the various

subgroups are summarized in Table 2.

The major observations are as follows:

d The small and unsystematic differences in Figs. 3–6

and the lack of excursions from linearity in the

combined scatterplot (Fig. 7) indicate the quality of

data from the Pisharoty sonde.

FIG. 4. As in Fig. 3, but for (a) pressure profiles at 1612 IST 10Dec 2010 and (c) pressure profiles

at 0449 IST 11 Dec 2010.



d Temperature data are matched with the data obtained

from imported sondes irrespective of the time of

ascent. This is evident from the small standard de-

viations and a high correlation value of 0.999 (Table 2)

across various subgroups.d Pressure data are also matched, especially at higher

altitudes (within 0.5 hPa), where the accuracy required

is higher. Scatterplot analysis also indicates a high

correlation of Pisharoty sonde pressure with that of

Vaisala, Meisei, and Graw.d It is uncertain whether the RH readings of the other

radiosondes are accurate. For example, according to

Vömel et al. (2007), Vaisala RS92 has a dry bias. This

uncertainty is the main reason why no RH corrections

are made, as stated in section 2a. Qualitative compar-

isons such as in Fig. 5 show that uncorrected Pisharoty

sonde RH readings still measure small-scale RH

variations similar to the other radiosonde in thin

atmospheric layers. The statistical study shows that

the sonde has good correlation with Vaisala and

Graw (Table 2).d Wind data from the Pisharoty sonde is closely (within

1ms21) matched with the data obtained from Vaisala

and Graw, as evident from Table 2. The correlation of

Pisharoty wind data with that of Meisei is slightly lower

when compared with that of other sondes. The large

FIG. 5. As in Fig. 3, but for (a) RH profiles at 1207 IST 11 Dec 2010 and (c) RH profiles at

1934 IST 11 Dec 2010. Pisharoty sonde readings appear more smoothed than other sonde

readings. Thismay be due to the 15-s averaging of Pisharoty sondeRH readings, while the other

sonde readings are not smoothed.



cluster of points along the diagonal in the scatterplot

(Fig. 7) indicates close agreement between sondes.

In addition to the comparison ascents, a 1-month oper-

ational test was performed by launching Pisharoty sondes

as operational soundings at the IMD Thiruvananthapuram

Observatory (WMOstation 43371) and transmittingWMO

TEMP messages over the Global Telecommunications

System (GTS) throughout February 2011. Preproduction

PS01_B3 radiosondes were used, the same as in the flights

listed in section 3b, but only preliminary solar radiation

corrections were applied, derived from the December 2010

and January 2011 comparison flights. Since no WMO in-

strument code is assigned for thePisharoty sonde, the 31313

group reported the five-digit system and status code as

59008, where 90 indicates an unspecified radiosonde.

4. Concluding remarks

ISRO-VSSC has designed and developed an ad-

vanced radiosonde system that provides a cost-effective

solution for atmospheric parametermeasurement.More

than 7000 sondes were produced and delivered to dif-

ferent user agencies for atmospheric modeling, meteo-

rological studies, and weather prediction.

Because of extremely low weight, the sondes can be

used with smaller balloons (less hydrogen–helium gas),

which eventually reduces the cost of the balloon ascent.

Another version (PS02_A1) of the Pisharoty sonde was

developed for wind-only applications, weighing around

75 g, which can be used to replace the optical-theodolite-

based tracking of balloons.

The Pisharoty sonde receiver has data storage facility

and is capable of an ac power supply or battery opera-

tion, and hence it can be used in remote locations. A

handheld version of the receiver is also developed.

After balloon release and real-time data acquisition, al-

ready recorded data can be replayed, if required, in the

software with another set of user-selectable parameters,

say, smooth lengths.A potential research application of the

system is the high-resolution boundary layer studies. In

FIG. 6. As in Fig. 3, but for (a) wind speed profiles at 1306 IST 10Dec 2010, (c) corresponding wind direction, (d) wind

speed profiles at 1612 IST 10 Dec 2010, and (f) corresponding wind direction.



addition to the usual balloon ascents, time-staggered as-

cents, which are essential for the day-of-launch wind bi-

asing scheme of launch vehicles, are also possible with the

Pisharoty sonde system. In this scheme, data from sondes

released every few minutes and captured by multiple re-

ceivers in the ground station allow for better atmospheric

modeling by making simultaneous measurements of wind

and atmospheric parameters at different altitudes.

This system has been validated by comparison ascents

from different places, during different seasons of the

year. The results have shown that the Pisharoty sonde is

a reliable and efficient system, best suited for atmo-

spheric studies, weather prediction, and other related

aerospace applications.

Acknowledgments. We would like to mention our

team members of Avionics at VSSC, who have shoul-

dered the responsibility of design and development of

the Pisharoty sonde system alongwith us:GopakumarR.,

Femina Beegum S., Eden Evans Samuel K., Binil Roy

T. S., Arun Alex, Mukundan K. K., Resmi R., and Satya

Bhushan Shukla.

FIG. 7. Scatterplots combining data from all the comparison ascents for (a) temperature, (b) pressure,

(c) RH, (d) east–west component of wind speed, and (e) north–south component of wind speed. PS01

represents Pisharoty sonde version PS01_B3 and Other Sondes refers to Vaisala, Meisei, and Graw.



We are grateful to the anonymous reviewers, who spent

their much valuable time reviewing and refining our paper.

We thank the team at the National Atmospheric Research

Laboratory (NARL) in Gadanki, IMD in New Delhi,

the Space Physics Laboratory (SPL) of VSSC, the Mete-

orology Facility (METF) Thumba Equatorial Rocket

Launching Station (TERLS) of VSSC, and the Kochi

Naval Base for their wholehearted support in conducting

the comparison ascents at these locations. We also thank

our colleagues at Satish Dawan Space Centre (SDSC)

in Sriharikota and various other centers of ISRO for

their valuable advice and support in system realization

and evaluation. Our sincere thanks are due to the di-

rector of VSSC for the inspiration and encouragement

provided during the various phases of systemdevelopment.

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