Corona Missions
Corona Reconnaissance Satellite
Corona is the name of a series of strategic reconnaissance satellites of the USA to acquire classified
photographic imagery during the Cold War period. The Corona program began on June 1959 and ended in
May 1972. Over this period, there were 145 Corona missions, of which 102 were successful. Altogether,
over 800,000 images were collected. Declassified on February 24, 1995, these photographs constitute a
valuable source of historical information for the study of environmental changes.
When the Corona satellite camera was first used, it only had a resolution of about 40 feet (13m). By the end of the program, the resolution of the satellite camera was enhanced to 6 feet (2m).
In the early missions, the satellite was orbiting at an altitude of 104 miles – 145 miles (160 km -180 km).
In later missions it orbited at a lower altitude of about 76 miles (121 km). The weight of the satellite was
about one ton during the early stage and rising to about 1¾ tons in the mid-1960s. The frame format of the
panoramic camera was about 2.18 inches x 29.8 inches (5.54 cm x 75.70 cm). Each frame covered a ground area
of about 8.6 miles x 117 miles (14 km x 188 km).
Films taken by the camera were contained in a capsule. The satellite was designed to de-orbit the film capsules
from space to earth near Hawaii. The film buckets were to be recovered in mid-air by a specially equipped aircraft
during their parachute descent. The buckets were designed to float on the water for a short period of time, so
that if the plane missed the buckets, navy ships can retrieve them, and then to sink if the recovery failed.
The Corona satellites were designated KH-1, KH-2, KH-3, KH-4, KH-4A and KH-4B. KH stood for "Key Hole”. The whole
program was operational over a 13-year period. The Corona photos presented on this chart were taken on December 13,
1969 with a resolution of 6 feet (2 m).
「科隆拿」偵察衛星
「科隆拿」是美國一系列戰略偵察衛星，在冷戰時期拍攝機密情報照片。「科羅拿」計劃是在1959年6月開始，並於1972年5月結束。在此期間，共有145次「科羅拿」任務，其中102次成功。總共收集了80多萬張照片。這些照片在1995年2月24日解密後，便成為一項有歴史價值的資料來源，可供環境變遷研究之用。
早期的「科隆拿」衛星所拍攝的照片分辨率只有40呎（13米）。到任務將結束期，其分辨率己提升至6呎（2米）。
在早期的任務，這顆衛星在104英里至145英里（160公里至180公里）高空的軌道運行。在後來的任務，它在大約76英里（121公里）的較低高度運行。衛星的重量早期約為1噸，在60年代中期提升至1¾噸。全景相機的框架格式大約是2.18×29.8英寸（5.54厘米至75.70厘米）。每個框架覆蓋約8.6英里 × 117英里（14公里 × 188公里）的地面面積。
該衛星的相機所拍攝的菲林貯藏在配有降落傘的密封箱內，在夏威夷附近上空便將菲林箱投返地球。在下降期間，一架配備了專門裝備的飛機在半空中回收這特別設計的菲林箱。它可以在水上漂浮一段很短的時間，以便飛機錯過了機會時，海軍艦隻還可以將它收回，如果海面回收再失敗，那麼就會沉沒水底。
「科隆拿」系统包括以下各式衛星: KH-1，KH-2，KH-3，KH-4，KH-4A和KH-4B。KH代表“鑰匙孔”，整個系统已運行了13年。這張圖表的「科隆拿」照片是KH-4型衛星在1969年12月13日拍攝的，分辨率為6呎（2米）。
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Landsat Missions
Landsat Earth Observation Satellite
Landsat was called ERTS (Earth Resources Technology Satellite) when it was first launched in 1972. This series
of earth observation satellites was renamed Landsat in 1995. Subsequently 7 satellites had been put into orbit
in succession. Landsat 5 was launched on March 1, 1984 and acquired colour images of only 30 m resolution.
Landsat-7 was launched on April 15, 1999 to collect panchromatic images of 15m resolution and multispectral
images of 30 m resolution. On May 31, 2003, the Scan Line Corrector of the satellite failed resulting in loss
of about 22% of the data in a single scene, although the satellite is still in operation. The satellite orbits
the Earth at an altitude of 705 km and revisits the same area at an interval of 16 days. Each scene acquired by
the satellite covers an area of 185 km x 170 km.
With Landsat 5 retiring in early 2013 and leaving Landsat 7 as the only on-orbit satellite, Landsat 8 was launched
on February 11, 2013 to ensure the continued acquisition and availability of Landsat data. Weighing about 2 tons
and orbiting at an altitude of 705 km (438 mi), the satellite carries Operational Land Imager (OLI) and Thermal
Infrared Sensor (TIRS). The OLI collects a panchromatic band of 15 m resolution and 7 multispectral bands of 30 m
resolution. The TIRS collects 2 thermal bands of 100 m resolution, but are resampled to 30 m in delivered data product.
Unlike the Corona satellite which captured imagery on photographic films, Landsat satellites carry sensors to collect
electromagnetic radiation reflected from the ground. The imagery is composed of a matrix of pixels. Each pixel
represents the amount of light within a spectral band reflected from the Earth's surface. Using various combinations
of spectral bands, different techniques of image processing and enhancement as well as merging of different remotely
sensed data, spectacular images can be generated to highlight particular features to facilitate interpretation and
analysis.
Landsat-8 collects 8 multispectral bands of which 4 are visible and 4 are beyond visible. In additional, it also
collects a panchromatic band and 2 thermal bands. An interactive tool to demonstrate band combinations is available
on line at www.geocarto.com.hk/band
Band Combination |
Applications |
5,4,3 |
Vegetation identification (Red in colour) |
5,6,2 |
Mangrove distribution (Dark orange in colour) |
6,7,4 |
Turbidity in reservoir (Light blue in colour) |
2,1,7 |
Newly built-up area (White in colour) |
地球觀察「陸地衛星」
「陸地衛星」在1972年首次發射時稱為「地球資源技術衛星」。在1995年，這一系列的地球觀測衛星改名為「陸地衛星」，隨後共有7顆衛星進入軌道。「5號陸地衛星」在1984年3月1日發射，收集30米分辨率的彩色圖像。「7號陸地衛星」在 1999年4月15日發射，能收集15米分辨率的全色圖像和30米分辨率的多光譜圖像。在2003年5月31日，該衛星的掃描線校正器失效，導致每景中約22％的數據丟失，儘管該衛星仍在運行中。「陸地衛星」在705公里的高度繞地球運行，並以相隔16天重訪同一地區。衛星收集一景的數據可覆蓋185公里×170公里的面積。
隨著「5號陸地衛星」於2013年初退役，並因「7號陸地衛星」是唯一在軌道上運作的衛星，「 8號陸地衛星」便於2013年2月11日發射，以確保「陸地衛星」數據可持續收集與供應。這顆衛重約2噸，在海拔705公里（438英里）的軌道上空運行，配有操作陸地成像儀（OLI）和熱紅外傳感器（TIRS）。 OLI收集15米分辨率的全色波段和30米分辨率的7個多光譜波段數據。 TIRS收集的2個熱能波段，分辨率原本是100米，但在交付的數據產品中重新調較至30 米。
「科隆拿」衛星拍攝的影像是顯示在菲林上。「陸地衛星」所拍攝的圖像是用傳感器來收集從地面反射的電磁輻射。圖像由像素矩陣組成。每個像素顯示從地球表面反射的光譜波段的光量。使用光譜波段的各種組合，圖像處理和增強的不同技術以及不同的遙感數據的合併，便可製成壯觀的圖像，突顯特殊的特徵，供解讀和分析之用。
「8號陸地衛星」能收集8個多光譜波段，其中4個是視覺範圍以內；另外4個是視覺範圍以外。此外，它還收集全色波段和2個熱能波段數據。 www.geocarto.com.hk/band的網站提供一個互動工具展示波段的組合。
波段組合 |
應用解說 |
5,4,3 |
植物辨別 (呈現紅色) |
5,6,2 |
紅樹林分布 (呈現深藍色) |
6,7,4 |
水庫混濁情況 (呈現淺藍色) |
2,1,7 |
新的建成地區 (呈現白色) |
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