Justice ERICKSON
delivered the Opinion of the Court.
We granted certiorari to review People v. Henderson, 847 P.2d 239 (Colo.App.1993), which involved the observations of a police officer from a television news helicopter of marijuana plants on residential property. The court of appeals held that the helicopter flight over the defendant’s property was not a search and that the warrant to search the defendant’s property was supported by probable cause. On appeal, the defendant claims that the court of appeals erred in determining that the news reporter who flew the helicopter could assert the Colorado statutory newsperson’s privilege and therefore was not required to testify at a suppression hearing. We affirm the judgment of the court of appeals.
I
In July, 1989, Officer Greg Bohlen, an undercover narcotics investigator for the South Metro Task Force, received an anonymous telephone call. The caller informed Officer Bohlen that Bernard Henderson had recently cultivated and sold marijuana from his residence at 4466 West Bowles Avenue in Littleton. The caller also stated that he observed $5,000 in cash, scales that are commonly used to weigh marijuana, and a number of weapons. Based on this information, Officer Bohlen placed the residence under surveillance for several days but did not observe any illegal activity.
On September 7, 1989, Detective Daniel F. Rupp received an anonymous call implicating Henderson in illegal activities. The caller indicated that Henderson lived at 4466 West Bowles Avenue, that there was Chevy pickup truck and a Harley Davidson motorcycle parked at the residence, and that marijuana was being grown in a shed behind the house. Detective Rupp conveyed this information to Officer Bohlen and the two officers went to the residence, walked around it, but saw nothing unusual.
Prior to September 8,1989, Officer Bohlen had attempted to secure the use of a helicopter for a fly-over of another location in an unrelated investigation. When he was unable to obtain a law-enforcement helicopter, Officer Bohlen entered into an agreement for the use of a helicopter operated by television station KUSA Channel 9. KUSA agreed to provide a helicopter to Officer Bohlen and Agent Dan Johnson so that the officers could take photographs of the location in exchange for the right to report on the drug investigation.
On September 8, the morning Officer Boh-len was to participate in the fly-over of the unrelated property, he received another anonymous telephone call from the same call[386]*386er regarding the alleged drug activity at 4466 West Bowles. The informant again indicated that he had been to the property and that Henderson was growing marijuana in a shed behind his house. The informant stated that Henderson retrieved a five-foot-tall marijuana plant from the shed and sold it to the informant’s companion for $500. Additionally, the caller informed Officer Bohlen that he was aware of a substantial drug deal that took place at Henderson’s residence a week prior to the call and that Henderson had automatic weapons in his house. As a result of the calls of the anonymous informant, Officer Bohlen asked the helicopter pilot for KUSA, Peter Peelgrane, if Peelgrane would fly him over Henderson’s house. Peelgrane agreed to fly over Henderson’s house after flying over the property that was the subject of the unrelated investigation.
Officer Bohlen, Peelgrane, Agent Johnson, and a photographer for KUSA made four or five passes over Henderson’s residence during a period of approximately five minutes. Officer Bohlen observed a shed to the south of the residence with a plastic roof “with green plant material growing underneath the plastic.” Officer Bohlen stated that the helicopter stayed between 500 and 700 feet in altitude. He based his altitude estimate on his experience flying in helicopters. Although he could not describe the plants in detail, based on his special education in drug identification and on his law enforcement experience, Officer Bohlen concluded that the plants were marijuana. Photographs were taken by the two police officers. Additionally, video tape was taken by the KUSA news photographer and was subsequently used in a news broadcast.
At about four o’clock on that same day, the anonymous caller telephoned again and told Officer Bohlen that Henderson had seen the helicopter fly over his residence and had ended his illegal gardening pursuits by uprooting and moving the marijuana plants.
The authorities subsequently obtained a no-knoek search warrant and seized evidence, including roots, stalks, leaves, and other remnants of marijuana as well as cultivation equipment and fertilizer. Guns, scales, plastic bags, a pipe, and a bag of marijuana were found inside the house.
On October 31, 1989, a felony complaint was filed in Arapahoe County Court charging Henderson with one count of cultivation of marijuana,1 and one count of conspiracy to cultivate marijuana.2 Henderson pleaded not guilty on April 20, 1990.
Prior to trial, Henderson issued a subpoena to Peelgrane in an attempt to elicit testimony from him at a hearing on a motion to suppress evidence. Counsel for KUSA and Peelgrane moved to quash the subpoena, invoking the newsperson’s privilege set forth in section 13-90-119, 6A C.R.S. (1993 Supp.). The trial court held that the privilege applied and quashed the subpoena. At the conclusion of the suppression hearing, the trial court denied Henderson’s motion to suppress.
Trial to a jury commenced on August 22, 1990, and on August 30, 1990, the jury returned a verdict of guilty on both charges. On December 19, 1990, the trial court sentenced Henderson to eight years on the substantive count and four years on the conspiracy count with the sentences to run concurrently.
Henderson appealed and the court of appeals affirmed the convictions. The court of appeals held that the fly-over by the KUSA helicopter did not constitute a search under either the Fourth Amendment to the United States Constitution or article II, section 7 of the Colorado Constitution, that the search warrant issued was not infirm, and that Peel-grane was protected from giving testimony by the newsperson’s privilege. People v. Henderson, 847 P.2d 239 (Colo.App.1993).
II
The court of appeals held that the fly-over was not a search under the Fourth Amendment to the United States Constitution and did not violate article II, section 7 of the Colorado Constitution. Henderson, 847 P.2d [387]*387at 241. Under the facts of this case, we agree.
A
The Fourth Amendment protects: “The right of the people to be secure in their persons, houses, papers, and effects against unreasonable searches and seizures.” U.S. Const, amend. IV. “The basic purpose of this Amendment ... is to safeguard the privacy and security of individuals against arbitrary invasions by government officials.” Camara v. Municipal Court, 387 U.S. 523, 528, 87 S.Ct. 1727, 1730, 18 L.Ed.2d 930 (1967). Therefore, warrants are generally required before a governmental agency or official may conduct a search. See United States v. Karo, 468 U.S. 705, 714-15, 104 S.Ct. 3296, 3303, 82 L.Ed.2d 530 (1984) (stating that warrantless searches are presumptively unreasonable).
A warrant is only required, however, when a search occurs. A search occurs when the government intrudes on an area where a person has a “constitutionally protected reasonable expectation of privacy.” Katz v. United States, 389 U.S. 347, 360, 88 S.Ct. 507, 516, 19 L.Ed.2d 576 (1967) (Harlan, J., concurring).3 See also California v. Ciraolo, 476 U.S. 207, 211, 106 S.Ct. 1809, 1811, 90 L.Ed.2d 210 (1986) (stating that a reasonable expectation of privacy is one that “society [is] willing to recognize ... as reasonable”); Karo, 468 U.S. at 712, 104 S.Ct. at 3302 (“A ‘search’ occurs Vhen an expectation of privacy that society is prepared to recognize as reasonable is infringed.’”) (quoting United States v. Jacobsen, 466 U.S. 109, 113, 104 S.Ct. 1652, 1656, 80 L.Ed.2d 85 (1984)). In order to determine whether the expectation of privacy is reasonable or “what expectations of privacy are constitutionally ‘justifiable,’ ” United States v. White, 401 U.S. 745, 752, 91 S.Ct. 1122, 1126, 28 L.Ed.2d 453 (1971), the facts and circumstances of each case must be analyzed to determine if the defendant’s expectation of privacy is objectively reasonable. See Oliver v. United States, 466 U.S. 170, 177, 104 S.Ct. 1735, 1740-41, 80 L.Ed.2d 214 (1984) (concluding that no single factor determines whether an individual legitimately may assert a claim under the Fourth Amendment that he should be free from governmental intrusion); United States v. Fisch, 474 F.2d 1071, 1077-78 (9th Cir.1973) (“The test applied as to society’s tolerance of the search rests, as it has for years, upon ‘the facts and circumstances — the total atmosphere of the case.’ There is no ready formula, ‘each case is to be decided upon its own facts and circumstances.’”) (footnotes omitted); Hoffman v. People, 780 P.2d 471, 474 (Colo.1989) (“The existence of a legitimate expectation of privacy must be determined after examining all the facts and circumstances in each particular case.”).
The United States Supreme Court applied the totality of the facts and circumstances standard to determine if a defendant had a reasonable expectation of privacy in Florida [388]*388v. Riley, 488 U.S. 445, 109 S.Ct. 693, 102 L.Ed.2d 835 (1988). In Riley, the Court determined that police observing the defendant’s backyard from a helicopter flying at 400 feet did not conduct a search for Fourth Amendment purposes.
The defendant in Riley lived in a mobile home located on five acres of property. Near the mobile home was a greenhouse that was obscured from view by a fence, trees, and shrubs. The contents of the greenhouse, however, were visible from above because two panels of the roof were missing. As the result of an anonymous tip, a police helicopter made two passes over the property at an altitude of 400 feet. The observing officer viewed what he thought was marijuana growing in the greenhouse. Based on the police officer’s observations and the anonymous tip, a search warrant was obtained and executed, and marijuana was found and seized. The Court held that the actions of the police officer did not constitute a search within the meaning of the Fourth Amendment. Id. at 450, 109 S.Ct. at 697.
A plurality of the Court concluded that one of the primary factors in determining whether the defendant’s expectation of privacy was unreasonable was that the helicopter was flying in navigable airspace within the Federal Aviation Administration (FAA) guidelines.4 Id. at 451, 109 S.Ct. at 697. Thus, the Court relied on the fact that the observation itself was legal. In Giradlo, the Supreme Court addressed the issue of the legality of a flyover. The Court held that an aircraft used to view the defendant’s backyard did not violate the defendant’s reasonable expectation of privacy because the police were in legal airspace at an altitude of 1,000 feet viewing what any member of the public could observe from an aircraft. The Court stated:
The observations by Officers Shutz and Rodriguez in this case took place within public navigable airspace.... That the observation from aircraft was directed at identifying the plants and the officers were trained to recognize marijuana is irrelevant.... Any member of the public flying in this airspace who glanced down could have seen everything that these officers observed_ [The defendant’s] expectation that his garden was protected from such observation is unreasonable and is not an expectation that society is prepared to honor.
Ciraolo, 476 U.S. at 213-14, 106 S.Ct. at 1812 (footnote omitted).
The Court in Riley also considered whether the defendant had a reasonable expectation of privacy based upon the intrusiveness of the observations. The Court held that there was only a minimal intrusion. The Court stated:
Neither is there any intimation here that the helicopter interfered with respondent’s normal use of the greenhouse or other parts of the curtilage. As far as the record reveals, no intimate details connected with the use of the home or curtilage were observed, and there was no undue noise, and no wind, dust, or threat of injury.
Riley, 488 U.S. at 452, 109 S.Ct. at 697. The fact that the helicopter circled twice over Riley’s residence and curtilage5 was not [389]*389found to increase the intrusiveness of the observation to such a degree as to constitute a search.6 In a broad sense, Riley and Cir-aolo recognize that ordinary unintrusive visual observations from public navigable airspace do not constitute a search under the Fourth Amendment.
Based on these considerations, the Court in Riley held that the defendant’s expectation of privacy in the contents of the greenhouse was not one that society would recognize as reasonable.
B
The instant case presents issues similar to those presented in Riley. First, according to the evidence, the KUSA helicopter was flying at an altitude of between 500 and 700 feet, which is a permissible altitude under current FAA regulations. See 14 C.F.R. § 91.79 (1988). In an affidavit in support of his motion to quash the subpoena, Peelgrane avers that he complied with all FAA regulations. Henderson presented no evidence that the use of the helicopter constituted a violation of FAA regulations.7
The critical aspect of this analysis is not the number of times the helicopter passed over the residence, Riley, 488 U.S. at 445, 109 S.Ct. at 693 (implying it was not dispositive that the helicopter circled twice), or the fact that it was a helicopter and not a fixed-winged aircraft, id. at 450, 109 S.Ct. at 696-97 (stating that the type of aircraft was not dispositive), or how often either military or civilian aircraft passed over the residence during the course of a year, id. at 451, 109 S.Ct. at 697 (noting that the greenhouse was not protected from “public or official observation”); rather, it is the fact that the marijuana was in plain view to anyone legally viewing the shed from the helicopter.8
[390]*390Second, the observation posed only a very limited degree of intrusiveness. The helicopter made approximately five passes over Henderson’s property over the course of several minutes and never flew below an altitude of 500 feet.9 There is little evidence of the noise, wind, dust, threat of injury, or interference with the use of the curtilage. In addition, the trial court found that there was no indication that other people in the neighborhood found the fly-over significantly intrusive to cause Henderson’s neighbors to come out of their homes in response to the helicopter.10 Cf. People v. Pollack, 796 P.2d 63, 65 (Colo.App.1990) (noting that during a fly-over at 200 feet, the noise from the helicopter caused six of the defendant’s neighbors to look at the helicopter).
After examining all of the relevant criteria, the totality of the circumstances indicates that Henderson did not have a reasonable expectation of privacy in his marijuana and therefore the fly-over did not constitute a search under the Fourth Amendment to the United States Constitution. Accordingly, we affirm the court of appeals on the Fourth Amendment issue.
C
Having determined that the fly-over was not a warrantless search proscribed by the Fourth Amendment to the United States Constitution, we review the claim of a violation of article II, section 7 of the Colorado Constitution. The additional analysis of the Colorado Constitution is necessary because the issue is one of first impression before this court.
Although this court, in construing article II, section 7 of the Colorado Constitution, has interpreted our state constitution as more protective of certain rights of privacy than some United States Supreme Court decisions addressing similar factual situations on Fourth Amendment search and seizure issues, see People v. Oates, 698 P.2d 811, 815-16 (Colo.1985) (beepers in commercially purchased items); People v. Corr, 682 P.2d 20, 27-28 (Colo.), cert. denied, 469 U.S. 855, 105 S.Ct. 181, 83 L.Ed.2d 115 (1984) (telephone toll records); People v. Sporleder, 666 P.2d 135, 140 (Colo.1983) (telephone phone records); Charnes v. DiGiacomo, 200 Colo. 94, 100, 612 P.2d 1117, 1121 (1980) (bank records), we see no reason to do so in this case.
We have held that a legitimate expectation of privacy is one that society considers reasonable. People v. Hillman, 834 P.2d 1271, 1273 (Colo.1992). We have also held that “the mere observation by government officials of that which is plainly visible to anyone does not constitute a search for constitutional purposes.” Hoffman, 780 P.2d at 473. Additionally, when analyzing search and seizure issues under both the federal and state constitutions, we have held that “in general, a [391]*391curtilage is not protected from observations that are lawfully made from outside its perimeter not involving physical intrusion,” and cited Riley and Ciraolo with approval. Hoffman, 780 P.2d at 474.
Henderson did not establish that the fly-over was so intrusive that it constituted a search. Accordingly, we hold that there was no search for purposes of article II, section 7 of the Colorado Constitution. Because the protections of article II, section 7 of the Colorado Constitution do not extend to investigative activity that does not amount to a search, Hillman, 834 P.2d at 1273, we affirm the court of appeals.
Ill
Henderson claims that the affidavit submitted by Officer Bohlen was insufficient to support a finding of probable cause. Henderson asserts that the search warrant therefore was not valid and that the evidence that resulted from the search of his residence should be suppressed. We disagree.
To support the issuance of a search warrant, the Fourth Amendment to the United States Constitution and article II, section 7 of the Colorado Constitution require probable cause and an oath or affirmation particularly describing the place to be searched and the objects to be seized. People v. Leftwich, 869 P.2d 1260, 1265 (Colo.1994). Probable cause for a search warrant exists when the affidavit in support of the warrant alleges sufficient facts to warrant a person of reasonable caution to believe that contraband or other evidence of criminal activity is located at the place to be searched. Bartley v. People, 817 P.2d 1029, 1033 (Colo.1991). To determine if probable cause exists, the totality of the facts and circumstances known to the officer at the time of the search must be considered. Illinois v. Gates, 462 U.S. 213, 103 S.Ct. 2317, 76 L.Ed.2d 527 (1983).11
The magistrate’s probable cause determination is given great deference and is not reviewed de novo. Spinelli v. United States, 393 U.S. 410, 416-17, 89 S.Ct. 584, 589, 21 L.Ed.2d 637 (1969); Leftwich, 869 P.2d at 1266. In reviewing of the determination of probable cause, we must be satisfied" that the magistrate had a substantial basis to rule that probable cause existed. Gates, 462 U.S. at 238-39, 103 S.Ct. at 2332; People v. Abeyta, 795 P.2d 1324, 1327 (Colo.1990).
Officer Bohlen’s affidavit relied on two types of information to establish probable cause: the anonymous informant’s tips and the information obtained from airborne observations. Under the totality of the circumstances known to Officer Bohlen at the time of the search, there was probable cause to issue a search warrant.
Under some circumstances, an anonymous informant’s tip alone will not satisfy the probable cause requirement. See Leftwich, 869 P.2d at 1266; People v. Diaz, 793 P.2d 1181, 1184-85 (Colo.1990). However, tips from an anonymous informant that have additional indicia of reliability or those that are corroborated may provide a substantial basis for a determination of probable cause. See People v. Paquin, 811 P.2d 394, 398 (Colo.1991); Abeyta, 795 P.2d at 1328-29. “Corroboration of an anonymous tip with facts learned by an investigating officer is sufficient for the practical, common-sense judgment called for in making a probable cause determination.” Diaz, 793 P.2d at 1183.
In this case, there were four anonymous tips. The informant described Henderson’s activities in detail, as well as property located at the Henderson residence. The caller specifically told Officer Bohlen that Henderson was growing marijuana in a shed near Henderson’s residence and that the informant had seen the marijuana. Although a “bare assertion of knowledge is not sufficient to establish an informer’s basis of knowledge,” Leftwich, 869 P.2d at 1266, Officer Bohlen corroborated the information with his own observations that marijuana was be[392]*392ing cultivated at the Henderson residence.12 Due consideration should be given to a law enforcement officer’s experience and training in evaluating the significance of the officer’s observations relevant to probable cause. Bartley, 817 P.2d at 1033. Additionally, although observation of plants growing in a shed may seem innocuous to an ordinary observer, this fact does not diminish the significance the observation would have to an officer trained and experienced in drug enforcement. People v. Hill, 690 P.2d 856 (Colo.1984).
In this case, the four independent, anonymous tips were specifically detailed and were corroborated through independent police observations. Additionally, the veracity of the tips was confirmed. Application of the totality-of-the-circumstances test announced in Gates establishes that there was a substantial basis for concluding Henderson was engaged in illegal activity and that drugs would be found at his property. Accordingly, we affirm the judgment of the court of appeals on the sufficiency of the affidavit supporting the search warrant.
IV
Henderson’s final contention is that Peel-grane is not entitled to newsperson’s immunity and therefore must testify at the suppression hearing regarding the altitude and flight pattern of the KUSA helicopter. In this case, the .record indicates that Peelgrane is entitled to the statutory newsperson’s immunity and that Henderson has not met the burden of proving an exception to the immunity. Accordingly, we affirm the court of appeals.
Section 13-90-119, 6A C.R.S. (1993 Supp.), which provides a “privilege for [a] newsper-son,” grants immunity to newspersons from testifying except under limited circumstances:
[N]o newsperson shall, without such news-person’s express consent, be compelled to disclose ... any news information received, observed, procured, processed, prepared, written or edited by a newsperson, while acting in the capacity of a newsper-son ....
§ 13-90-119(2), 6A C.R.S. (1993 Supp.). The statute broadly defines “newsperson” to include any member of the mass media and/or any employee who is engaged to “gather, receive, observe, process, prepare, write, or edit news information.” § 13-90-119(1)(c), 6A C.R.S. (1993 Supp.).
For purposes of the statute, Peel-grane was acting as a “newsperson” when he piloted the helicopter. § 13-90-119(1)(c), 6A C.R.S. (1993 Supp.). Peelgrane was employed by KUSA as a full-time reporter and his reports were regularly featured on KUSA news broadcasts. KUSA assigned Peelgrane to observe and gather information regarding the police attempts to uncover illegal drug activity. Although Peelgrane was also the helicopter pilot who flew the police officers over the Henderson property, he was acting as a newsperson as defined by subsection (l)(c), and not as a police agent.
The statute defines “news information” as:
[A]ny knowledge, observation, notes, documents, photographs, films, recordings, videotapes, audiotapes, and reports, and the contents and sources thereof, obtained by a newsperson while engaged as such, [393]*393whether such items have been provided to or obtained by such newsperson in confidence.
§ 13 — 90—119(l)(b), 6A C.R.S. (1993 Supp.).
The information garnered by Peelgrane falls within the statutory definition of “news information.” § 13-90-119(l)(b), 6A C.R.S. (1993 Supp.). Henderson sought to have Peelgrane reveal the altitude of the helicopter and its flight path to help establish that Officer Bohlen was conducting a search. Peelgrane’s observations and knowledge of the altitude and flight path of the helicopter are protected by subsection (l)(b). Statutory privileges must be strictly construed. People v. District Court, 743 P.2d 432, 435 (Colo.1987).
Although the newsperson’s privilege is broad, the statute also sets forth several situations in which the privilege does not apply. For instance, section 13-90-119(2)(a) through (d) provides that the privilege of nondisclosure does not apply to information that is: (1) received at a press conference; (2) published or broadcast;13 (3) based on a newsperson’s personal observation of a crime, when such information cannot be reasonably obtained through other means; and (4) based on a newsperson’s observations of a class 1, 2, or 3 felony.
In addition to the specific instances in which the newsperson’s privilege does not apply, the statute provides a method to subpoena a newsperson at a hearing on a news-person’s motion to quash the subpoena. In order to defeat the privilege, the party issuing the subpoena must show, by a preponderance of the evidence, that: (1) the information sought from the newsperson is “directly relevant to a substantial issue involved in the proceeding,” (2) the information “cannot be obtained through any other reasonable means,” and (3) a strong interest of the party issuing the subpoena outweighs the interests of the newsperson and the public under the First Amendment to the United States Constitution. § 13-90-119(3), 6A C.R.S. (1993).
In this case, Henderson has failed to show that he could not obtain the evidence requested from some other reasonable means.14 For example, the question of whether the airspace over Henderson’s property was restricted, or was a no-fly zone, could be answered by calling an FAA official to testify or by subpoenaing FAA records. Additionally, testimony regarding the altitude of the helicopter was given by both Henderson and Officer Bohlen. In fact, Officer Bohlen testified that during the flight, the altitude was discussed and that the helicopter’s altitude was at all times between 500 and 700 feet. Officer Bohlen also stated that he was experienced with helicopters and was able to estimate altitude.
Given that Peelgrane was operating as a newsperson, his observations and knowledge of the flight path taken to the area, and the altitude of the helicopter, were protected under the statute. The record reflects that Henderson did not meet his burden of establishing that the privilege should be waived or limited. Because we hold that Peelgrane is entitled to the newsperson’s privilege in this case and that Henderson failed to meet his burden of proof to overcome the privilege, the trial court did not err by granting Peel-grane’s motion to quash the subpoena summoning him to testify at the suppression hearing.
V
Under the facts of this ease, the fly-over did not constitute a search, the warrant was valid, and Peelgrane was properly granted [394]*394newsperson’s immunity. Accordingly, we affirm the judgment of the court of appeals.
LOHR, J., dissents, and KIRSHBAUM, J., joins in the dissent.