The capabilities of the calculated approach for the astroclimatic assessment in radioastronomy

doi:10.4236/ns.2010.25052

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Vol.2, No.5, 427-431 (2010) Natural Science

http://dx.doi.org/10.4236/ns.2010.25052

The capabilities of the calculated approach for the

astroclimatic assessment in radioastronomy

Nikolay V. Ruzhentsev*, Alexander S. Mihailov

Department of Microwave Radiospectrometry, Institute of Radio Astronomy, National Academy of Sciences, Kharkov, Ukraine;

*Corresponding Author: [email protected]

Received 30 December 2009; revised 3 February 2010; accepted 25 February 2010.

ABSTRACT

The work is dedicated to calculation of daily

variability of monthly averaged full vertical at-

mospheric absorption for six well-known moun-

tain locations of sub-millimeter wave band ra-

diotelescopes obtained with usage of chosen by

authors models combination. Test locations we-

re defined as follows: Chajnantor plateau in the

Atacama mountain desert (Chile), Hanle (India),

South Pole (Antarctic), Mauna Kea (Hawaii,

USA), Sierra Negra (Puebla, Mexico) and El

Leoncito (Argentine). The data of these calcula-

tions were compared with the data of long term

radiometric observations of other authors. Se-

arching for new alternative places to comple-

ment existing sub-millimeter telescopes loca-

tions was attempted too.

Keywords: Radiotelescopes; Atmosphere

Absorption; Sub-Millimeter Waves Range;

Astroclimate

1. INTRODUCTION

Earth atmosphere causes considerable impediments for

radioastronomical observations at millimeter and sub-

millimeter waves bands due to atmosphere attenuation

and instability its transfer function. Consequently, even a

slight improvement of the transfer function and its sta-

bility can lead to a tangible radioastronomical observa-

tions efficiency increase, especially in the submillimeter

wave range. In view of this and taking uniqueness and

high cost of the radiotelescopes that are installed in

various regions of the world, location astroclimatic suit-

ability assessment is required. These assessments are

usually experimental and consist of gathering the statis-

tical information concerning the extent of atmospheric

attenuation, it’s seasonal and daily unsteadiness to reveal

the most favorable time and place for the observation to

be performed [1-5]. A few only places with most suitable

for allocation of sub-millimeter waves radiotelescopes

are known [6] to the present time in a world. It is Cha-

jnantor plateau in the Atacama mountain desert (Chile),

Hanle in the Chanthang mountain plateau (India), South

Pole (Antarctic) Mauna Kea (Hawaii, USA). The un-

questionable advantage of the experimental approach is

the precise measurement of the atmospheric attenuation

in the defined frequency range in the defined location.

However, the most significant disadvantages of this ap-

proach are the fact that only a limited set of frequencies

is used for the experiment (usually 1 or 2 frequencies)

[1-4], the necessity of continuous observations cycles

that last several years, financial, hardware and organiza-

tional efforts and expenses of this important, but yet

auxiliary support for radioastronomic observation.

On the contrary, analytical astroclymatic assessment

approaches could provide operative and cheap daily and

seasonal unsteadiness prognostication for any millimeter

and submillimeter wavelength in any location of the

world. However, there was an impediment on the route

to the practical implementation of this approach: There

were no adequate models of global distribution of mete-

orological parameters altitude profile that were required

for this kind of astroclymatic assessment until present

days. The purpose of this work is the finding and dem-

onstrating new possibility (unavailable earlier) of ob-

taining of astroclimatic estimations of atmospheric at-

tenuation average values by calculated method, as well

as definition new locations of radio telescopes (most

favourable for radioastronomical observations) of sub-

millimetre range.

As we have shown recently in [7-9] (on the example

of 15 regions of Ukraine) utilization of the chosen com-

bination of Liebe’s atmosphere attenuation model and

the latest meteorological atmosphere standard (grounded

on the ERA-15 base data) [10-12] allows us to acquire a

good (within the 10% precision interval) harmony of

analytical calculations and experimental data concerning

the monthly attenuation average in the atmosphere above

the plain-type landscape. It is also very important for

certain applications that the chosen models combination

N. V. Ruzhentsev et al. / Natural Science 2 (2010) 427-431

428

allows the atmospheric absorption variability prognosti-

cation for different times of day. However, mentioned

above application of models need to be considered for

the mountainous landscape also because a great amount

of radiotelescopes at millimeter range and especially

submillimeter range are located up to 5 km above the sea

level.

This work contains the calculation of daily variability

of monthly averaged full vertical atmospheric absorption

using the chosen model combination for six well-known

mountain locations of submillimeter waverange radio-

telescopes. Test locations were defined as follows: Cha-

jnantor plain in the Atacama mountain desert (Chile,

5000 m), Hanle (India, 4500 m), South Pole (Antarctic,

2800 m), Mauna Kea (Hawaii, USA, 4100 m), Sierra

Negra (Puebla, Mexico, 4600 m) and El Leonsito (Ar-

gentina, 2500 m).

Data from these calculations were compared with data

of long period radiometric observations (from one year

up to nine years) of other authors. Searching for new,

alternative or other places to complement existing sub-

millimeter telescope locations was attempted.

2. RESULTS OF CALCULATIONS

AND ITS COMPARISON WITH

EXPERIMENTAL DATA

Figure 1 displays analytically acquired dependencies of

monthly average full vertical atmospheric absorption

values on the UT time of day for Chajnantor during

January and July on the frequency of 225 GHz.

International astronomic submillimeter waverange ob-

servatory (ALMA) is located on the height of 5 km

above sea level. Nine years cycle atmospheric absorption

yearly observation results for the frequency of 225 GHz

[1] as well as the results of our calculations are displayed

on the same figure.

Figure 2 displays the calculated dependencies of the

full vertical atmospheric absorption on the UT time of

day for Hanle during January and July on the frequency

of 220 GHz. Indian astronomic submillimeter waverange

observatory (IAO) is located on the height of 4.5 km

above sea level in the Hanle. Atmospheric absorption

year cycle observation results for the frequency of 220

GHz taken from [2] are displayed on the same figure.

Figure 3(a) display analytically acquired dependen-

cies of monthly average full vertical atmospheric ab-

sorption values on the UT time of day for EI Leoncito

during January, February and July on the frequency of

405 GHz. EI Leoncito is an Argentinean-Brazilian

sub-millimeter wave range radiotelescope located on the

height of 2.5 km above sea level. The results of one-year

cycle of atmospheric absorption observation for 405

GHz frequency taken from [4] are displayed on the Fig-

ure 3(b).

Figure 4(a) display analytically acquired dependen-

cies of monthly average full vertical atmospheric ab-

sorption values on the UT time of day for South Pole

during January and July on the frequency of 225 GHz.

American Antarctic remote observatory with a sub-mil-

limeter wave range radiotelescope (AST-RO) was lo-

cated in the South Pole on the height of 2.8 km above

sea level. The results of half-year cycle of atmospheric

absorption observation for the 225 GHz frequency taken

from [3] are displayed on the Figure 4(b).

In the Figures 1-4 the rather close layout of data cal-

culated by us and points taken from the literary data [1-5]

is well visible for radio telescopes in El Leoncito Argen-

tina (405 GHz), on South Pole (220 GHz), in Hanle

(220 GHz), in Chajnantor (225 GHz).

The differences of calculation data and data of ex-

periments, as a rule, are concentrated in the interval of

(a)

(b)

Figure 1. Calculated dependencies of the daily

changing of the monthly average values of full verti-

cal atmospheric absorption (a) as well as the results

of our calculations (bold curve) and experimental

observations [1] (square) of monthly averaged values

of vertical atmospheric absorption (b) for the Cha-

jnantor (225 GHz).

N. V. Ruzhentsev et al. / Natural Science 2 (2010) 427-431

429

(a)

(b)

Figure 2. Calculated dependencies of daily

changing of the monthly average values of full

vertical atmospheric absorption (a) as well as

the results of our calculations (bold curve) and

experimental observations [2] (squares) of mon-

thly averaged values of vertical atmospheric

absorption (b) for the Hanle on the frequency of

220 GHz.

10-20% in the winter and 20-30% in the summer for the

year courses of monthly average values of vertical ab-

sorption of atmosphere on all of selected by us radiote-

lescopes. (The separate summer month only takes place

an exception in Chajnantor and in Hanle, when these

differences are noticeably higher.) Our calculations of

diurnal variability have completely qualitatively coin-

ciding with experiment and differed quantitatively from

experiments less than on 15-20%.

Let’s remark that it would be possible to expect a de-

creasing all these 10-30% values of differences in a case

of more correct comparison of calculated and experi-

mental data. The absence of complete correctness in rea-

lization of such comparisons is caused by different peri-

ods of averaging for different literary experimental data

and data of our calculation during definition of monthly

vertical absorption values of atmosphere. The values of

this parameter calculated by us were based on the data of

fifteen-years meteorological observations, while the ex-

perimental values reduced in the literature were obtained

by averaging from radiometer data for one of separated

years only.

Influence of above-mentioned cause is well visible,

for example, on dispersion of experimental values of

monthly average absorption defined for different years

in the Chajnantor (Figure 1) or in the Hanle [2]. The

small differences (less than 15%) between data of our

calculations (averaged for fifteen-years term) and ex-

perimental average-year values of absorption in Mauna

Kea [5] (averaged for eleven-years term) as well as be-

tween experimental data for Sierra Negra [13] (averaged

for four-years term) shows a validity of such point of

view.

Besides it is necessary to take into account that the

experimental measurements were carried out not always

in the conditions of completely clear atmosphere. But

nevertheless a carried out qualitative and quantitative

(though upper estimations) rating of errors of considered

(a)

(b)

term of observations: 28 February-1 March

Figure 3. Calculated dependencies of daily changing of the

monthly average values of full vertical atmospheric absorp-

tion (a) as well as the results of our calculations of monthly

averaged (gray curve) and daily experimental observations

(squares) values of vertical atmospheric absorption [4] (b)

for EI leoncito observatory on 405 GHz.

N. V. Ruzhentsev et al. / Natural Science 2 (2010) 427-431

430

(a)

(b)

Figure 4. Calculated dependencies of daily changing

of the monthly average values of full vertical atmos-

pheric absorption (a) as well as the results of our cal-

culations of monthly averaged (gray curve) and daily

experimental observations (squares) values of vertical

atmospheric absorption [3] (b) for South Pole on the

frequency of 220 GHz.

by us method of astroclimatic forecasting is visual and

useful enough (Figures 1-4).

3. SEARCH FOR ALTERNATIVE AND

ADDITIONAL RADIOTELESCOPE

LOCATIONS

The results that were acquired in the previous section

demonstrated an efficiency, high operability and func-

tional capabilities of calculational approach to astrocly-

matic assessment. At the same time, analysis of the most

successful locations of operational sub-millimeter wave

range radiotelescopes from the astroclymatic point of

view [6] allows us to note that out of four radiotelescope

locations two are situated in the southern hemisphere

(one in the Andes and one in the Antarctic) and two in

the tropics of the northern hemisphere (in the Hawaii

and in the Indian part of Chanthang mountain plateau).

And the most notable locations of southern hemisphere

are distinguished by being more seasonally stable and by

a smaller optical thickness value than in the northern

hemisphere. According to our calculation (Figure 5) we

can note that the best location in the astroclymatic point

of view would be southern pole where monthly-average

atmospheric absorption values () are two-three times

less than, for example, for the Mauna Kea or in the

summer months for the Chajnantor.

Seasonal vertical atmospheric absorption variability is

characteristic for every sub-millimeter wave range ra-

diotelescope location, but in different degrees. In con-

nection with that, the best radio astronomical observa-

tions from November to April can be made in the South

Pole, Hanle and Mauna Kea, while from May to October

they can be made on the South Pole, Chajnnator and

Mauna Kea (Figure 5).

Mentioned alternative locations or complementary

locations (Russian Altay, Rocky Mountains in Colorado,

New Earth in Russia, Greenland, Chines Gobi desert,

Tibetan Chanthang plateau, etc.) were chosen by us for

consideration on the common physical grounds (altitude

above sea level, latitude, climate peculiarities). The com-

parison of result calculations that were carried out for

these new places allowed us to distinguish only three

astroclymatically suitable locations to compete with best

known locations.

These are: Greenland (H = 2,2 km, 80 N, 40 W), Chi-

nese part of Chanthang plateau (H = 5 km, 33 N, 94 E)

and Altay (H = 3 km, 50 N, 88 E) (Figure 6). For exam-

ple, first two locations are not inferior to and even better

than the South Pole and the Hanle from November to

April.

It is noticeable that their monthly-average atmospheric

absorption value and seasonal variability is almost iden-

tical (Figure 5 and Figure 6) between the one in the

Chajnantor (ALMA) and found location on the Green-

land (if corresponding seasons are compared for north-

ern and southern hemispheres). Moreover, calculations

Figure 5. Annual changing  for the most known locations of

radiotelescopes of sub-millimetre waves.

N. V. Ruzhentsev et al. / Natural Science 2 (2010) 427-431

431

Figure 6. Annual changing  for the new found locations

which are suitable for radiotelescopes of sub-millimetre waves.

show that optical atmospheric thickness daily deviation

is almost absent in the Greenland during all year while

this value reaches up to 50% in summer in the Chajnan-

tor (Figure 1(a)).

Comparing data on Figure 5 and Figure 6 allows us

to note noticeable (almost twice) astroclymatic condi-

tions increase while shifting on the Chanthang plateau

from Hanle (India, H = 4.5 km, 32 N, 78 E) to Tibetan

location (H = 5 km, 33 N, 94 E) which is situated on the

same plateau, but on the Chinese part of it. The same

situation is observed while shifting from El Leoncito

(Argentine) in the Atakama to the Chajnantor in Chile.

However, this case is also affected by the altitude dif-

ference of these locations.

4. CONCLUSIONS

Thus, for the first time is shown that usage most of

modern standard of atmosphere (designed by ESA on the

basis of the database ERA-15) in aggregate with МРМ

model of atmospheric attenuation allows to obtain a

seasonal-diurnal statistics of vertical atmospheric ab-

sorption for any item of a world. Such possibility of the

calculated method was shown as by comparison of the

original data of calculation with the experimental data of

other authors, as and by definition new astroclimatically

favourable locations of sub-millimetre radiotelescopes.

This new and previously unavailable ability to obtain

astroclymatic assessments of  ensures high operability,

functional abilities increase and minimal expenditures in

comparison with the traditional approach that is based on

long-term experimental observations (which usually uses

to choose the location of the projected radiotelescope or

to specify astroclymatic assessment in the locations of

operated radiotelescopes).

REFERENCES

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